Well, we had a slightly impromtu test of the new FB2700 3G dongle support last night when BT had some issues.
Sadly this happens, and is why we offer things like dual line (2xBT), and dual line (BT+Be) type services. DUal line tends to be a bit expensive for home users though. However the FB2700 has a USB port and over the last few days the new s/w releases have included the 3G dongle support (at last).
One of our customers has been testing this and was suitable impressed :-
"Very impressed to see the FB2700 fall back to a routed IPv4 block over 3G, when BT tripped over a cable this evening! I only noticed 10 minutes after my main connection died when I happened to glance at the CQM graphs on the FB2700."
By default the support allows simple NATted (yes, I said it) routing over a single IP on a generic 3G dongle which is ideal as a backup. However when used with A&A data SIMs it allows the backup to be for the DSL line, handling routing of the block of (legacy) IPs to the dongle when the line is down... His irc session did not even drop!
Seems this "just worked".
Thanks to "tgb" in A&A irc for confirming.