Hi,
This looks like an interesting project.
We have been developing low power, 3.3V Arduino solutions along the same lines as you do, but using the Fio and Stalker boards.
We however have been using the mobile phone network (GPRS) for data transfer. This gives of course a much greater coverage.
For this purpose we have developed a GPRS module that fits in a bee slot.
Would you be interested to try one on your board?