Uses a standard DTMF (Tone Dial) phone for programming at any one of extension 601-604 for model SP-416C.
Model SP- 416C (4 CO lines + 16 extensions) Compact Home / Office Telephone System, 1 to 4 incoming phone lines, up to 16 extension lines, internal and external phone to phone calling and transfer, on hold, etc, simple setup, check out the manual at
http://www.soho-pbx.com/Manuals/pbx%20308C-416C-432C-832C-manual_rev_2.pdf
Collect it for free or will ship for £10.00 UK Royal Mail Next Day
Note : The Door Phone Feature is not enabled on this model