you hope to accomplish getting a better signal...faster data speeds... and better battery life. youi could experience all these thing if you update also it does not conflict with a custom or stock rom when you change the radio because updating a radio does not hard reset the phone. if i were you i'd try some different radios and see which one i like best. some of the popular ones are the sprint 1.11 and the telus as well as the us celluar. check out this thread
http://forum.ppcgeeks.com/showthread.php?t=46616