e61
Key features:

* Rich connectivity options - UMTS, Wi-Fi, Bluetooth, USB, Infrared
* Outstanding battery life
* 2 megapixel camera
* Messenger form factor with a full QWERTY keyboard
* Really large 2.8" TFT display
* Solid, metallic body
* Symbian OS 9.1 S60 3rd Edition UI
* microSD memory card slot

Main disadvantages:

* Hefty weight
* No HSDPA support
* No secondary camera for video calls
* S60 UI doesn't come with Feature Pack 1

p990i
Main advantages

* Autofocus 2 megapixel camera with macro mode and LED flash
* Memory stick Duo/PRO Duo memory card slot (hot-swap)
* Walkman MP3 player and stereo FM radio with RDS
* 3G support with video calls, GPRS and HSCSD
* Wi-Fi 812.11b support
* Touchpad TFT display with a QVGA (240x320 pixels) resolution
* Stereo Bluetooth 2.0, Infrared port and USB 2.0 support
* Conventional keypad on a removable flip along with a QWERTY keyboard
* Internal 128MB flash memory and 64MB RAM
* Symbian 9.1 OS with the UIQ 3.0 user interface

Main disadvantages

* Incompatible with older Symbian UIQ applications
* No EDGE support
* Records video with a QVGA 320x240 pixels resolution
* Display not very legible under direct sun light
* User interface is not always user-friendly
thanks 2 gsmarena.com