I read that the T-mobile network supports 1000K (1MB) picture messages, and so the Motorola Cliq XT will automatically resize larger pictures to conform to this limitation when you attach them to a message. Unfortunately, the ATT network is reported to still be limited to 300K messages, so your picture messages will not be delivered to your friend's iPhone on the ATT network, unless you can attach smaller pictures.
As for apps, I do not use a task manager or task killer, as some of these actually seemed to cause my Cliq XT to run slower and use more battery power. I personally have found that the Android OS manages apps just fine on its own.
As for my favorite apps, I continue to be amazed at the number of free, very useful, and well-designed apps that I am able to download and use regularly. I have settled on about 40 so far! A few of my free favorites in no particular order: AppBrain App Market (which allows easy management and sync of my phone's Apps through a simple web browser interface on my my PC); "Backflip Light" (which allows me to use the camera's LED flash as a bright flashlight); White Noise Lite (which acts as a "sound machine" for masking background noises with rain/beach/train and other soothing sounds when I sleep or study); Timeriffic (which allows me to schedule certain phone functions such as automatically putting the phone ringer in silent mode when I sleep); Bubble Level (a very accurate electronic level, handy for picture hanging, etc.); myRemote (allows me to remote-control my Home Theatre Media Center PC from my phone); Google Sky Map (I can finally identify all of the cool things I see in the night sky simply by pointing my phone at the sky); SIPDroid VoIP (my cell phone acts as an actual business telephone extension to our office SIP phone system over WiFi and 3G); Pandora Radio (customizable commercial-free streaming music anywhere); PicSay Photo Editor (powerful photo image editing right on the phone);TV.com (free streaming of TV shows for added entertainment on-the-go); GPS Essentials (a suite of powerful GPS/location tools including accurate electronic compass, customizable dashboard displaying speed/altitude/location/direction/etc., GPS mapping, waypoint management, view of GPS satellite location/strength, camera view of your target destination); ConvertDroid (every conceivable measurement conversion); KeepScreen (allows control over display screen sleeping, easily allowing automated control over which apps need to have screen stay on bright when in use); Alice (keeps me informed about tour dates and local performances by my favorite bands); OurGroceries (allows synchronized shopping lists between all family members so as to avoid duplicate or missed item purchases); Places Directory by Google (easily find and get details about local banks/bars/restaurants/shopping/gasoline/attractions and more); EStrongs File Explorer (for easy file management of my SD card); EasyTether Lite (useful for connection of my laptop PC to the internet via my phone's internet connection, admittedly a slow connection but very useful in rare instances when I must connect to the server at work over VPN).