After serious thinking Jose wrote :[color=blue]
> On 21 Mar 2008 10:03:09 GMT, alexd <troffasky@hotmail.com> wrote:
>[color=green]
>> A) Some kind of hosted centrex system, where you pay a fee per month per
>> extension, and you register every extension with a central server on the
>> internet[/color]
>
> I've already considered that, but I trying to avoid multiplying the
> number of ATAs in the office
>
>[color=green]
>> B) SIP-capable PBX on site. This will involve a bit more work and
>> expertise on your part, but [depending on how many extensions are
>> involved] could lower costs and increase reliability.[/color]
>
> Can you name one? I've already googled it, but it all seems rather
> strange, at this stage[/color]

Commercial:

<http://www.drogon.net/dsx/features.html>

<http://www.provu.co.uk/protalk_pbx.html>

Homebrew:

<http://pbxinaflash.net/downloads/>
[color=blue]
>
>[color=green]
>> If you've got a spare PC, you could test out scenario B with PBX In A
>> Flash [pbxinaflash.net], as it will likely work with the ATAs you already
>> have.[/color]
>
> I'll investigate.
>
> Thanks a lot!
> Jose[/color]