Here in Denmark it's $30 for a data-only HSDPA plan with a transfer limit of 10GB per month, so the idea of having HSDPA built-in would be to replace the need to have a mobile phone and never have to pay voice and sms fees again.

It would require also that the device stay connected to be able to ring on incomming IP packets on certain protocols such as VOIP, IM, push email notification and such while the rest of the device should be in sleep mode.