if i unlock a t mobile sidekick 3 will it work on cingulars network with aim, yahoo, and msn messenger ?

Sorry, but with T-Mobile, you can't get a SIM unlock for Sidekick Devices. This is because only T-Mobile offers the Sidekick internet service, and using the phone on another network still costs T-Mobile money. Best bet if you want the Sidekick III (which by the way is a SWEET device) is to get a plan with T-Mobile. You can get a basic plan for as low as 29.99 for 300 anytime minutes and unlimited weekends, or 39.99 for either 600 anytime minutes with unlimited nights and weekend or just straight 1000 anytime minutes, then add the sidekick plan for 20.00 or you can do the data only plan for 29.99 a month. It is definitely a great deal. You can check the coverage in your area too at www.t-mobile.com. Just click on the coverage link and enter your address...it gives you an accurate idea of what the coverage in your area is like. Good Luck!!

Yes you can you just have to get the phone unlocked or buy one off of ebay unlocked the only problem is you won't be able to go online because T-mobile uses Dangers, servers and Cingular dosen't. The only thing that you would be able to do is Text and Call that is it! Hope this info will help you out :)