I'm on the verge of going with VoIP Unlimited, porting over my 80 DDI's from British Telecom, and as of mid September they stated they could not provide T.38 until British Telecom correctly supported it on their IP backbone
Although being on their doorstep you could give them a nudge for us, wink wink.
Now I think about it, and I sincerely hope I get corrected by someone in the know, no provider in the UK can provide T.38 that goes out successfully to a PSTN.
T.38 to PSTN is what we realy want as otherwise it's no use.
Thought I'd post an update in case anyone in the UK is interested.
VoIP Unlimited do now provide T.38, which I've been testing over the past couple of days to and from faxes on PSTN lines (fax machines are connected to 3CX using Linksys SPA3102's), and it works flawlessly so far !.
No additional costs at all, it's part of their standard SIP Trunk service.
Their call costs may not be the cheapest for some destinations, we call customers all over the world, but their trunks are very cheap and for a single monthly price you have unlimited channels on your trunk.
Our 3CX system is going live this morning after months of testing, so get ready for me to change my mind later today
If anyone in the UK is interested due to poor lead times with obtaining an new analogue line from O2 (using BT Openreach) I've had to setup a 3Cx v11 server using VoIP-Unlimited as the SIP trunk provider as they support T.38 faxing.
As I couldn't source any Linksys SP3102's at the time I went with Cisco SPA112's, which support T.38
Out of the box the SPA112 would receive fine but not send, updated to the latest firmware, v 1.2.1 from v 1.0.1, there are loads of T.38 fixes and it now works brilliantly