Here are my suggestions based on the type of operating system (OS) you prefer:
- Apple iPhone OS: You only have once choice here. Apple iPhone. If you're tight on cash, you'll be able to find a used iPhone 3G. Good luck getting a new iPhone 3G[S] by July 1.
- RIM BlackBerry: Storm (or Storm 2 if you can wait until after July 1. This is coming later this summer).
- Google Android: T-mobile G1 (there are other phones coming later this summer)
- Palm WebOS: Palm Pre
- Palm Original OS: Used Treo (why buy a device that's running a dying operating system?). Avoid the Palm Centro.
- Microsoft Windows Mobile OS: this is where things get really complicated. There are several new phones coming out later this summer, so if you can wait, then you'll end up with a much nicer phone. If you prefer something like an iPhone, then go with something like the Samsung Omnia of HTC Touch Diamond . If you prefer a slider, then go with the HTC Touch Pro (or Touch Pro 2 or Samsung Omnia Pro).