I'd be curious to know if the throttled performance with the 5GB prepaid plan is any different than the throttled performance with the 3GB post-paid plan (the one that I'm on, and which supports conditional call forwarding, for make benefit glorious Google Voicemail services). I suspect they're the same.

Cris's MiFi idea might be a great way to go, particularly if you can populate it with one of those pre-paid 5GB/mo SIM cards. Then, you've got your extra bandwidth that you can easily switch to and share with others.