I just had some thoughts about Kindle tethering that could be another opportunity for Amazon.
Why the roaming data charges are so high? Because telecoms of various countries do not want to cooperate. Travelers usually solve this issue by buying a separate pre-paid SIM card for each country they visit but can it be done with one single sim card? Probably not but do we really need an actual sim card? After all a sim card only provides authentication keys that could be emulated by software. A tablet device could provide data connection specific to each network by local contracts and low local prices. In essence it would be like Skype but for 3G data.