Hi,
I've converted a 7140 annex B to annex A as described in several posts over here.
Does it work : yes
Do you get a good result on ADSL2+: no
I've an ADSL2+ Annex A line with a distance of 3,4 km and with a -native- Annex A Speedtouch 780 WL I get a synch down/up speed of 7Mbit/1.1Mbit...