First point - you cannot use the POTS line unless you buy an OBi 110, or you have that line separate from your other phones. The 100 and 202 don't connect to a POTS line.
Second point - how many of your house phones are plugged into the wall? Many people have a portable phone's base station plugged in to the POTS line, and then all the portables around the house that aren't plugged into to anything but A/C.
If you buy the 110, you can do as ProfTech says and determine your UVerse wiring. If on the outside of the house they split the wiring in the box into Uverse and phone, and those two wires then come into the house, one way to handle things is to then find that POTS (plain old telephone service) wire that comes into the house, which likely connects to a small junction box, which then feeds your phone outlets in your house. At that junction box, you would remove the wires feeding the rest of the house and plug in a phone cord that then would plug into the LINE port of the 110. You would then plug the phone outlet lead into the PHONE port of the 110, thereby supplying every phone outlet in your house with both the OBi VoIP lines as well as the POTS line.
THIS IS THE CLEANEST SETUP.If AT&T did not split the line outside the house, they MIGHT have brought it in as one line with the DSL portion (or UVerse) on two of the four wires and the phone as the other two of the four wires. If they did this, then you need to determine which two wires feed the DSL and which two feed the phone line (likely Red and Green). You could then split that wire in the OBi / Uverse room into two plugs, one feeding the Uverse modem and the other feeding the OBi line port, and then plug the base of a portable phone into the OBi phone port.
A more complicated scenario would depend on how your house is wired. Some houses have one wire that goes from one room to the next through the entire house. Some houses have a separate wire in each room, fed from the junction box in the basement. If you have the first scenario, then you could put the OBi in the first room on the circuit with the incoming red/green (assuming I was correct above) wires hooked to one phone jack, feeding the OBi's LINE port. You could then take the red/green wire that feeds the next room and hook it to a separate phone jack right below, and plug the OBi's PHONE port into that. In this way, the OBi would power all the phone outlets in the house with both VoIP and POTS.
I found it much easier to put everything in the basement on the wooden board that my electric box and phone junction is on, everything except for my wireless router (so I get max signal on the living floors). My phone wire comes in from AT&T (now disconnected) and feeds the LINE port of my OBi 110, which then feeds all the house phone outlets with the PHONE port. I also installed my AT&T DSL modem there (now replaced by a cable modem). The DSL modem fed, via ethernet, my wireless router. The wireless router then goes back down to the board and feeds a ethernet switch, which then feeds ethernet in several rooms in the home as well as the OBi 110, providing the VoIP signal which is then sent through the phone wire. Sounds complicated, but in fact is quite straighforward.