>>Hi Michael,
>>
>>>We have a building with one of those phone keypads in the vestibule that calls a residential phone number. The answerer can then chat with the caller and then can buzz them in by pressing a key combination into their keypad.
>>>
>>
>>So, the existing system uses an internal phone system? What make/model?
>>
>No, it just uses the local carrier - no seperate system.
>

Then Centrex is probably used - the door being another 'extension' in the building group.

>>>We need to upgrade this system. I can figure out how to do the dialing part, but how do I watch for the tone combination from the tenant in order to activate the door lock - and what do I use to activate that door latch?
>>>
>>
>>Your need a device to decode the DTMF tones - something the existing system does very nicely :>) Door opening is a matter of solenoid activation by the decoding device. I don't see this as much of a VFP project as a bolt in hardware solution. This kind of system is 'off the shelf'.
>>
>>>Any references out there on this type of project?
>>
>>Tons. http://www.google.com/search?hl=en&q=keyless+door+entry
>>
>Thanks...
>>>Michael

With no inhouse switching matrix (key system or PBX), the system in place is undoubtedly the simplest and cheapest way to go. There must be a box on the premises that answers on dialing the open code - activating the unlock. That box and your phone company is the system. I'd leave it alone :>)