iPhone 3GS for $149
Hit the link to see it. Cowboom.com has them refurbished for $149. I can unlock them for you for $10 when you sign up for service.
Remember that on our service, 3G on iPhone is not available in all areas. Check user reports in my blog post. Your data speeds will be slower, but you can always use WiFi at the home / office instead plus that is much faster.