I've got a Grandstream HT-503 that I use as a gateway between my PSTN and my internal 3CX system. 1) I'm not happy with the sound quality of calls via the HT-503. What I don't know is if it is possible to tweak some settings that will help or if it is just-the-way-it-is. Any clues, anyone? 2) When receiving calls I don't get the caller's ID coming through. I just get the SIP id of the HT-503 which is 10000. I've examined the packets coming from it to the PBX and they've got 10000@<ip address> in them. I've search the web for appropriate settings to make it work but nothing has worked, so far. Does anyone here have a HT-503 (or similar) that they've got caller id working with on a UK line? The line is operated by Zen Internet - I don't know if that makes a difference vs. British Telecom. My current settings are below: Thanks.