I used to have it. I think there is a 'keep alive' option in the settings on the 2wire modem (I had an actiontec modem).Sadly that wont do any good as I said I can be ssh into the box and be typing away at command prompt and my connection drops and I have to wait 60 seconds to get back in and the modem has a new IP.
If not have the box you're sshing into ping google every minute or two (ping -c 20 google.com) via a cron job.