Here's another consideration. Simplexity operates Wirefly as well as the miles-earning portals.

A new Motorola Droid for Verizon at MileagePlusWireless.com is $150 and gets you 5000 United miles. At Wirefly.com, it's $100 and no miles. In other words, you're paying a penny a mile.

Wirefly and the other 3rd party dealers are usually cheaper, but impose additional terms (like a $200 penalty for changing anything on the account in the first 6 month).