[tnkgrl] has concluded her Sony Vaio P by adding GSM support. We covered the switch to XP earlier, but this should work on Vista too. The Vaio P is sold in the US with support for Verizon’s EVDO wireless broadband, but it uses the same hardware as the European model that uses GSM. This is possible because of the the Qualcomm Gobi radio module. To get GSM support, you trick the VZAccess Manager into loading a different firmware than the stock EVDO. The difficult part is that the Vaio P doesn’t come with a SIM card slot, so you’ll have to solder in your own. When you’ve got the computer reassembled, just change VZAccess Manager to use your carrier.
UPDATE: Wired has an article on the Gobi chipset.