I've used Boost before. It worked great for me. If you want a better phone than the Walmart kind for Boost, get a Motorola i885. It's a great phone for Boost - but they're hard to find.
http://cgi.ebay.com/NEXTEL-MOTOROLA-I880-I-880-PHONE-AS-I885-IN-BOX_W0QQitemZ260509169122QQcmdZViewItemQQptZCell_Phones?hash=item3ca78e75e2
Boost is the Pay as you go plan for Nextel / Sprint. So, you can check a coverage map for your area.
They have a monthly Unlimited Plan for $50:
http://plans.boostmobile.com/monthlyunlimited.aspx
