I've got a Treo 755P... the Smartphone

Phone, camera, PDA all in one. I think it does music and video, too... I don't use it for that, though.
My thoughts... you can't go wrong (really!) with just getting an intro-level phone. Look in the Sunday paper for whoever's offering a free phone for a two-year signup and take it.
Ask about plans, though. There's generally a *HUGE* penalty for going over your minutes, and minimal impact for going under them. Not everyone rolls them over every month, but you may not need that. My wife's phone originally was just 25 minutes a month... emergencies only, basically. That was around $15/month, IIRC.
Just did a quick Google...
www.letstalk.com offers a plan comparison site that's based on your ZIP code. Take a look there to see what the options are, and remember... the plan is what continues from month to month. The phone cost is a one-time thing...