I just got a Motorola Bravo (android) from Consumer Cellular last week and have been thrilled with the phone and the service. CC is a prepaid/no contract service that offers monthly payment tiers of voice and data. They resell on the AT&T network. You select a voice and data tier separately, so you can go super low on voice since you don't use it much, and higher on data. The voice and data plans I selected will total $25 a month, and that's not even the lowest tiers. Plus they notify you by email if you are approaching your monthly limit so you can temporarily go up to the next tier to avoid overage charges.
After using the phone for about a week I'm very pleased. I selected this particular phone because it has WiFi (not all smart phones do) which saves huge on data charges when I use it at home or a friend's house. And I downloaded an app to locate free WiFi when out and about, although I haven't tested it yet. I plan to use the WiFi when traveling outside the U.S.
The Bravo allows you to play mp3's, but I don't use that functionality.
I investigated the Tracfone prepaid service which is a prepaid 'pay for every minute and text' offering. I believe it would be slightly cheaper than Consumer Cellular, but I didn't want to get annoyed if I got silly text messages from someone (like my young niece) knowing that I would get dinged $0.10 for each one.
My previous phone was a Blackberry with Verizon service. That monthly plan was $80 per month, which includes a corporate discount. Now that I have switched to my $25 a month plan with CC, I actually gained functionality with the droid and pay much less in monthly fees. Note I paid up front for the Motorola Bravo, which was $190 including taxes.
CC forgot to load the voicemail number on the phone's SIM card. I tried to report the problem using their online web form and didn't get a response within 24 hours as promised. I eventually located an 800 line for service on the welcome letter, and my call was answered immediately and the service agent fixed the problem straight away.