I am experimentally rolling out hosted VoIP in around ten small offices in the UK and Europe and one or two in North and Central America, but I am dogged by call quality issues in some locations whereas in other offices it's almost faultless. Some calls simply cut off, which I gather is most likely to be a NAT Proxy related issue, and some calls are really distorted and broken, which I gather is most likely a network connection/packet loss/latency issue. Strangely the remoteness of the geographic location does not always correlate with poor service.
As we need to make use of the Asterisk PBX, all the traffic is directed through the hosted VoIP servers in London as opposed to going point to point once connected. Obviously this adds to the call quality problems in certain locations. Also most of the handsets are behind firewalls using NAT so a NAT proxy is required which, as i understand it, further adds to the problems.
I know that the simple answer should be to install a Asterisk box on each site, but I'd like to avoid this if at all possible especially as some offices only have 2 or 3 extensions, and I have not found a cheap enough piece of hardware which will manage the site and that can have an IAX trunk to our provider.
I have been using Linksys SPA941 & SPA942 handsets and am really happy with them. Routers vary office to office and the internet connection is mostly ADSL & SDSL, but as I say there are realtively few extensions and internet demand from other devices in the offices is minimal.
ALL tips and pointers are extremely welcome!