I use AT&T myself. I have a 29.99/month plan and I paid (after rebates) $49.99 on my cellphone (Nokia 8265, love the blue background light).
So its 29.99 a month and 49.99 for your cell-phone. If you sign a 2-year contract, the activation fee is waived (which is what I did). Just go to
www.attwireless.com and look up their cell phone/plans.
Hell, use google.com and type in 'cell phone plans' - that is how I learned the basic shiat.