Also considering buying from a retailer thats not your phone's carrier like:
AmazonWireless: Cell Phones, Cell Phone Plans, and Accessories
I think saden has bought from costco with bettter/cheaper results. I have Verizon and always thought i had to buy through them for my upgrades and renewels, which is not true you can buy from anywhere.
I recently got a 4g phone and would say get a 4g phone. Youre locked into this thing for 2 years so you might as well have something youre not going to be fustrated with in 6months a year.
Also i feel like most 4g phones run faster on wifi, only because they are built to run at faster speeds on a continueing basis. At least that has been my experience.