You think that's good - their BT Business Broadband Voice is even worse! If you're registered on their system as using one piece of kit (like one of the older modems they supplied) if you attempt to use your own VoIP kit through your own gateway, quite often you only get half-duplex communication! There's something up with the way BT's hardware handshakes with the VoIP kit; when I set up a VoIP kit at a local business I found that if I rang people they could hear me but I couldn't hear them. I had to ring the BT BBV helpline and tell them the exact model number of the VoIP gateway hardware I was using in order for them to make a config change on their end to make it work properly.
The reason I didn't cotton on to this earlier was because the router was actually handshaking and registering (apparently) correctly with BT's SIP gateway, which was a real pain because I couldn't figure out what the hell was up until I rang and explained the problem (and got an "ohhhhh I know what the problem is" from the CSR). Also, If you try to use the site listed on their documentation to configure your account, it doesn't work properly with your web browser - you type in your IP phone number (0560x xxxxxx) and password and it opens the next page on the site, then you click Next and it opens a popup... And shows a "system error, please try later" message! This'll happen every time if you left click, you have to RIGHT click on the Next button and open in a new window for it to work... Nice going BT! And THEN, if you aren't using your IP kit through a godforsaken HomeHub (the kit I was setting up was all Linksysco (Cisco branded as Linksys as I call them now)) you have to extract the correct config details from the URL string passed to the browser by the web site to input into your equipment to make it register with BT's SIP gateway correctly!
Oh, and the password they give you on the piece of paper... Utterly useless, because the BBV web site actually rehashes the password and the SIP gateway only accepts THAT version... And it passes not just one but TWO (different) proxy servers through the browser string which the HomeHub is configured with, but which there's no other way of viewing unless you dissect the URL string to find out what they are. Very nice job there!
The call drops on BT Broadband Voice just sound either like problems with your line or due to congestion in general on the network, and it's something I wouldn't be surprised at at all given BT's oversubscription of their residential broadband network. It really annoys me that you HAVE to have a BT broadband line to receive anything like an IP service or their new TV service, how utterly pointless is that. They'd make far more if they resold their services and just routed them all over their IPStream networks (which just about every UK ISP uses for backhaul anyway, which is why most UK ISPs have ludicrously low bandwidth caps due to the high price of wholesale bandwidth!) grrrrr BT make me so angry