That sounds like the Zoom 4300 BT modem, which is still available on Amazon at
http://www.amazon.com/Zoom-Wireless-...5293952&sr=8-7

Amazon's title just calls it a fax modem, but if you read further down the page you can see that it works for dial-up internet as well. That listing has used items only.

Unused ones can be bought at a much higher price under a different Amazon listing:
http://www.amazon.com/Analog-Modem-B...p_ob_e_title_1

Like mdanehart, I bought mine on eBay. I don't find any on offer there today.

EDIT, 2012-01-01:
Sorry, I didn't notice that I was replying to a post more than three years old. The thread came up on the first page of the N810 forum, so I just assumed it was an active topic. It seems that someone revived it for reasons unconnected with the earlier posts in the thread.