The software of the phone is:
UC Software Version 18.104.22.16834
We have had nearly 8 months of ongoing tests with BT, the issue seems to be worse when at peak times, for example we had no connections today (the first day back after a bank holiday) until lunch time, also, when sudden bursts of traffic occur in our own office we sometimes get drop outs too.
Last week however we had zero drop outs, but that is not very often, on average we are 70% down at all times.
BT have recommended a new non BT router as a last resort, but the pattern I feel could suggest our local exchange/line on our entire trading estate might be spiking …but BT say this is not the case, so who knows.
Its either the line in to us, or the router blocking us, one or the other.
Just to conclude this entry, we resolved this issue after nearly 9 months by switching from a BT Router to a Dray Tek. This router is far more capable to handle web traffic and priorities connections, and this seems to have pretty much fixed our phone problem.
Whether the BT router simply didn’t work with the Cloud Phones, or our local web traffic was too high/ congested for the router to handle with the phones we will never know.