Well I have had my new line order provisioned early and it's up and running...
Last time I tested an OBiLINE adaptor it was with a Virgin Media PSTN line and back then I was using a completely different OBi202 and a completely different OBiLINE adaptor - I had no issues back then! (No echo or random DTMF tones during calls)
Well I have just hooked up another OBi202 & OBiLINE adaptor to a working BT line and configured it as per this guide
and so far it's working flawlessly. All I have did was upload the latest UK XML file to the OBi202 while it had the OBiLINE connected and configured SP1 with Voicehost, SP2 with Voicehost, SP3 with Voipfone and SP4 with FreePBX.
The result? No echo and no DTMF tones being played back (for now at least). will see how it goes! Out of interest would anyone who suffers from this issue be willing to send me a backup of their OBi's configuration? The OBi doesn't backup any passwords so there is no security risk in doing so, would like to upload it to my OBi202 and test again.