T-Mobile unveiled pricing changes late last year. AT&T and Verizon announced price changes this month. Carriers don't do much to make details very simple and comparing them can be frustrating.
BillShrink.com has what they call The Ultimate Cell Phone Plans Comparison. The chart lists details on various plans offered by Verizon, AT&T, Sprint and T-Mobile. It never hurts to shop around.
Check it out here.