going retro...old-fashioned modem???

I often travel with my laptop, and would like more flexibility in how I use my modem.

I'm sure there's at least one or two of you out there who remember the old days, when you set the handset into the modem's cradle...allowing it to "talk" through the phone handset's built-in mic and speaker...this would be back in the Commodore/Trash-80 era.

Obviously you can't connect at lightning speeds doing this (it's kind of lossy), but I'm trying to determine if it would be possible. The idea is: design a small mic & speaker that can be stuck onto the handset of any phone. Then find (or make) a "driver" to allow windows to see the sound card as a modem.

Anyone know of any existing technology similar to this?
Anyone think I'm crazy?

Some of the newer cell phones have an attachment that makes that allows you to hook directly into a USB port.

Is this what you're looking for?

similar. I'd like the flexibility to dial up using a hotel phone, or even a pay phone, though.

Not to mention...my nokia has no data hookup (at least no data cable is available), but it *does* have a headset jack.