(Pleas note: the features were all from Wikipedia)
iPhone OS 2.0 (or iOS 2.0): Pay $9.95 to upgrade an iPod Touch Added language support Norwegian, Swedish, Danish, Finnish, Polish, Dutch, Korean, and Brazilian Portuguese language interface in iPhone, previously these languages were only in the iPod Touch since 1.1.1 Extra keyboard languages including Chinese and Korean and Russian Support for Traditional and Simplified Chinese handwriting recognition Mail, contacts, calendars Grouped settings Mail Push e-mail Ability to select an outgoing email account within Mail application Support for BCC in Mail application Multiple email delete/move Ability to view MS Office attachments Ability to view iWork attachments, including Pages, Numbers, and Keynote Contacts Contacts icon on "Home" screen (iPhone only, it was formerly on the iPod Touch) Ability to search contacts Global Address List Push contacts Ability to import SIM contacts Calendar Multiple calendars supported in Calendar with color coding (desktop colors only preserved if using Mobile Me) New "Calendar" menu in Settings Push calendar Enterprise enhancements Enforced security policies Device configuration Remote wipe iPod Video can be shown in either landscape orientation (instead of just landscape left) Videos in playlists & music videos can be shown in portrait or landscape orientation Sound fade-out when exiting a video Other App Store (to manage third-party applications) with home screen icon- Store for apps. Certificates and Identities WPA2/802.1X Ability to turn Wi-Fi back on while in Airplane mode Cisco IPsec VPN support Ability to take screen captures Ability to save pics from Safari or Mail to Photos Bonjour service discovery protocol Support for SVG Addition of Parental controls Password letters are momentarily visible while typing Ability to turn Location Services on or off Applications that use Location Services now prompt user for confirmation 3 times. Tapping status bar to scroll to top shortcut Updated calculator with extra features in portrait mode, a scientific calculator in landscape mode and an updated icon. Updated iTunes with a new icon and reordered category icons within iTunes application. Camera now supports Geotagging YouTube plugin for Safari
iPhone OS 2.0.1 (or iOS 2.0.1): Bug fixes Performance and stability of Contacts and Calendar applications dramatically improved Performance while flipping to landscape mode in Safari improved Performance in Mail app improved Release improves application crash rates Keyboard responsiveness improved
iPhone OS 2.0.2 (or iOS 2.0.2): Improved communication with 3G networks Transition from music list to Cover Flow has changed. Tilt to left from landscape no longer switch to portrait when watching video, fixes 2.0 bug The "Update All" button in the App Store's update tab has been removed
iPhone OS 2.1 (or iOS 2.1): Free for iPod Touch users who have upgraded to iOS 2.0. Initial Release on iPod Touch 2nd generation (as 2.1.1) Companion Changes in/with iTunes 8 for this release Displays capacity and used space of information on iPhone. Dramatically reduced time to back up to iTunes Does not remove all media after restore Faster firmware installation and data sync Application updates downloaded from iTunes have new finder naming convention Bug fixes, performance enhancements Security fix to prevent from bypassing the double home button exploit Fixed bugs causing hangs and crashes for users with lots of third party applications Faster installation and updating of 3rd party applications Updating applications keeps their icons in place on the home screen. Improvements to Mail stability Improved email reliability, notably fetching email from POP and Exchange accounts Faster loading and searching of contacts Auto-correct now appears above the text instead of below (fixing a usability problem people were having where auto-correct would appear above the first row of keys). Smoother browsing in Safari, particularly when scrolling up/down on a web page Significantly better battery life for most users Decrease in call set-up failures and dropped calls Improved accuracy of the 3G signal strength display. Some Bluetooth headsets which didn't originally work with visual voicemail on previous firmware versions have been reported to be working on 2.1. The 12/24 hour clock which has been available in previous versions is now usable to UK iPhone users. Improved way of creating the "Application Map" on reboot fixes the "ALoD" issue. Third-party application settings are loaded after loading the main Settings. With the UK English keyboard setting, when entering URLs, holding down the '.com' button would bring up shortcuts to other TLDs, but for some reason it would drop '.net' to make room for '.co.uk'. 2.1 adds '.net' for the UK English keyboard. Apple have fixed the grammar in the App Store when all apps up to date. Before 2.1, the update page would display the text "All Apps Are Up-To-Date." (hyphenated with a period). The update page now displays the text "All Apps Are Up to Date". Double tapping (the standard gesture for zooming) didn't work in prior firmware versions in the Mail application. The only way to zoom into content (e.g. a HTML attachment/web page) was to use the 'pinch' method. 2.1 now adds the functionality of double tapping to zoom in the Mail application. Calculator bug fixed affecting calculations involving Pi. OS enhancements Triple-click on the control button of headphones now jumps music to previous track played. SMS app can alert up to two additional times if you don’t acknowledge an incoming text message. (will play the alert sound/vibrate again after a period of time as if a new message just came in). When receiving a text message, it used to display "Sender — Text Message" when the message preview was off, e.g. "Pete — Text Message". After updating to 2.1, it now just displays "New Text Message". Update Supporting Languages Option to wipe data after ten failed passcode attempts. (After 5 attempts, the device will disable itself for 1 minute. After the 6th attempt, it will disable itself for 5 minutes. In the 10th attempt, it will wipe all data.) 3G, EDGE, and GPRS indicators changed. The camera can now be turned off within the restrictions page. When taking a screen-shot of your phone, there is now the camera shutter noise Pause apps by clicking the icon while it downloads/installs Updated apps now keep their original position in the Home Screen. iPod volume/application volume setting is now independent of the phone ringer volume setting. iPhone never gets locked when placed in dock and play music. New application features Genius playlist creation More information provided within iPod Music lists (artist and album are now shown below song title when selecting music in addition to remaining time on podcasts) More information is provided for audiobooks, such as displaying time left in active audiobook. New podcasts & videos had "filled" blue bubbles next to them to indicate that they were new, but with 2.1, if you have "half-played" a podcast or video, it will include a half filled blue bubble. Sound from iPod now "fade out" if you start syncing device with iTunes. Options to load & display earlier text message in a conversation. EXIF data information now remains on photos/pictures when emailed from your iPhone. Sites such as Flickr are now able to show geotag and other information. When location services is switched off in the Settings menu, the Maps application reminds you to manually turn it back on from the Settings menu when using GPS. Originally, you would have the option to turn it on when the notification appeared. Bookmarked home screen apps open in full screen. Only available in the iPod Touch Settings for individual speaker sounds. Sounds can no longer be turned off en masse. All sounds must be turned off individually to mute sounds. New speaker sound when sending mail. Only available in the iPod Touch 2nd generation Nike+ Support
iPhone OS 2.2 (or iOS 2.2): Free update for iPod Touch owners that upgraded to iOS 2.0. Enhancements to Maps (iPhone only). Google Street View Public transit and walking directions Display address of dropped pins Share location via email Cache of recent locations Enhancements to Mail Resolve isolated issues with scheduled fetching of email Improved formatting of wide HTML email App Store changes "Categories" section has been altered to display icons instead of a list. Individual applications pages now have 'Tell A Friend' and 'Report A Problem' buttons. In an app's description, multiple screen shots can now be viewed, instead of just one. "Update All" button added to "Updates" section. Option added to rate an application that is about to be deleted. Improved touch response when purchasing or downloading an application. Application icons display the install progress "in place" while updating, rather than on the last position of the page. Safari enhancements Improved stability and performance of Safari Layout changes for the address bar in Safari iPod Player changes The edit/clear icons on the on-the-go playlist have been changed. Podcasts now are being shown in catalogs. You can not delete audiobooks anymore through the device. Audiobooks without artwork, are now shown with a book icon and not with a note icon. Contacts improvements US phone numbers now display correctly e.g. 1111 2222 (In 2.1, this would have been shown as 1 111222 2). Other enhancements Podcasts are now available for download or stream in the iTunes application (over Wi-Fi and cellular networks) Decrease in call set-up failures and call drops Improved sound quality of visual voicemail messages Visual voicemail unavailability is shown in a screen instead of voicemail button not working Improved performance overall, especially noticeable in Notes and Camera applications. Emoji for SoftBank users in Japan. Can be enabled in all other countries using apps from the App Store. Pressing the Home button from any Home screen takes you to the first Home screen. Preference to turn on/off keyboard auto-correction New languages are supported. Shows Update/Restore progress when update using iTunes Security improvement Developers can pipe video out to an external device. Better shift-key behavior Automatic WebClip icon change Locked screen screenshots Ability to record from devices connected through the dock port Some minor bug fixes and improvements. Picker sounds are now controlled by the keyboard sound settings Macworld OTA updates iTunes now works over EDGE and 3G networks and no longer needs a Wi-Fi network iPod Touch 2nd generation only Line-in audio has been enabled through the headphone jack. Add the Remote button to control other devices (Like Apple TV, ...) on the Nike + iPod menu.
iPhone OS 2.2.1 (or iOS 2.2.1): Improved general stability of Safari Fixed issue where some images saved from Mail do not display correctly in the Camera Roll Updates Baseband iPod Touch only Fixed issue that caused some Apple Lossless (ALAC) audio files to skip during playback iTunes 8.1 Fixes calendar color syncing issue (Mac only) Uses a new baseband which patches the exploit previously used to unlock the iPhone 3G.
This is the only iOS version that requires payment for updating to iOS 2.0.