If you are thinking about Sprint, make sure you get one of the newer MIDP 2.0 phones. You'll need to install your apps over the air for testing but there are lots of tools around that make that pretty easy. I offer one at my website.
Not many Sprint phones will install MIDlets over a cable. The Treo's will do this. There's a program called BitPim that will install MIDlets on some Sanyo phones. The LG-325 has Bluetooth but you can't push MIDlets to it.
Personally, I think Sprint is the best US carrier for hobbists. There's poor developer support but you can at least install applications without begging for Nextel's permission.
For people who are actually trying to make money, use Verizon's BREW system instead. You'll never sell much on Sprint.
William Frantz
http://sprintdevelopers.com