EarthLink Wireless Service with Treo%u2122 650 - FAQ
Earthlink is a national ISP; they bought Mindspring back in the 1990s. MindSpring was the second ISP I used (I started out with an obscure company in Colorado back before commercial ISP services were really established); I still have a Mindspring address and thus a connection to Earthlink.
Earthlink now sells cellular service. They're not so different from Sprint, except they have better data plans. I suspect they're using Sprint's network; they're CDMA and the coverage map looks like Sprint's (there's no analog roam though!). I'd give it a look, except I'm waiting to see what Apple does in the next 2-3 months.
They feature the Treo 650 and the BlackBerry 7250.