Instant messaging:
If you need access to more than one instant messenger from your smartphone, try Beejive (
http://www.beejive.com). This nifty little application can aggregate your IM account from multiple services, including Yahoo!, AIM, Google Talk, Windows Live Messenger, and more. Also available for BlackBerry, Beejive sports a very intuitive and easy-to-read interface, and with it, you'll be able to keep track of multiple conversations from multiple services at once.
Forums:
Tapatalk (
http://www.tapatalk.com) has quickly gained popularity as a web forum reader, and for good reason. First, for those forums that have integrated the code necessary for them to become Tapatalk-enabled, it does away with the forums' bulky web interface and puts the primary content - discussions - in a phone-friendly format. Reading topics becomes a simple matter of scrolling through the threads, and of course you can create new threads or respond to existing ones directly from your phone.
Right now Tapatalk is available for iPhone, Android, Nokia, and - in beta - BlackBerry. Once installed, you can use the application to browse for forums by topic, sign up, and start talking.