2-Wire 3800HGV-B bridge mode

I have AT&T U-verse internet and TV using the 2-Wire 3800HGV-B modem. I’m also using T-Moble’s VOIP for home phone which uses the LinkSys WRTU54G-TM router. I’m having trouble with the T-Mobile router frequently going off-line with lengthy off-line times. Some times for a couple hours. Unplugging router corrects the problem. T-Mobile support recently informed it’s because U-verse frequently changes IP addresses and the Linksys adapter has trouble re-synchronizing. To correct the problem, I was told to change the 3800HGV modem to bridge mode so the IP address will be passed to the LinkSys modem. What are the procedures to change the 3800HGV modem to bridge mode?
Larry, Michigan