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As is so often the way, I took the challenge and got a result, not ideal, but a result all the same!
I managed to pick up a second hand PBX system and installed it....
It works a treat, unfortunately it was previously used at a russian hotel or something and a lot of the extensions personalised settings are passwrod protected (of course I don't know the passwords and neither does the vendor!). It's quite amusing, but not too professional when clients call!
Any advice ona master reset for a BizFon system appreciated! (I've downloaded all user guides, but no luck yet!).