I’ve been using T-mobile for years. Great service. I’m on a grandfathered $50/mo 2GB/tethering plan (throttles after 2GB). Nice thing is that data is free but slow abroad, and I could even use VoIP to make calls from Dom Rep to the states.
Pre-paid doesn’t have int’l data free, but is cheaper ($35-45/mo vs $70/mo for their current post-paid plan). Then there’s MetroPCS, which can be had for $25-30/mo, no int’l data, taxes included. $30/mo on Metro includes 2GB/mo.