After a bit more digging, Sprint's PCS Vision terms say that no networked devices are allowed.

T-Mobile seems to have it (T-Mobile Internet is the feature name apparently), but T-Mobile still doesn't have a great network, and they're the last of the big providers that charges domestic roaming. That's a bad combination in my book.

Cingular tells me that Media Net is the right answer from them for connecting a laptop to the internet. $19.99/month unlimited on top of the voice service. They told me they "don't support bluetooth" but it'll work with a data cable. I see no reason why it wouldn't work with bluetooth also, the configuration is the same once the devices are paired, right?