If you don't have a smartphone at all, I would recommend going through craigslist and look for one. Craigslist is great for cells cause people are always upgrading so you get newish phones for a discount. For budget android smartphones I personally like the Optimus T and you can often find used around $50 and it works with T-Mobile.
T-mobile prepaid is great, if you only need a few days you can get their "Pay by the day" $2/day unlimited voice/text/data for edge speed or $3/day for 4g
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Just buy a T-mobile SIM card ($1.99) and you can activate it with one of these plans and put in $10 or $20 (enough to cover the number of days youll use) prepaid card. The time does expire, but you don't use it up unless you use that phone that day. We did this last time and put in $10 for 5 days we were there cause we don't have data.