Has anyone configured an analogue telepone adaptor as a sip extension to allow the connection of a standard phone?

I would think you could with a 3rd party sip license....

Thanks in advance

Hi Bushmills

You just need a 3rd party SIP extension licence and MGI channel, it is trial and error because each device is different but I have used Cisco ATA's and Polycom Soundstations with no problems. Make sure you only set this up on a LAN if you value security.
In the device just look for Outbound Proxy and Registrar address type in the systems IP address. Then Identification or Account details, Display Name/Auth User ID type the extension number and Auth Password.