On 09-06-2015, at 3:35 PM, Louis LaBrunda <Lou at Keystone-Software.com> wrote:

> Hi All,
> 
> It is my understanding that one can use the GPIO pin(s) of a Raspberry Pi
> to detect the caller id information of an incoming phone call.  Does anyone
> have any experience with this?  Can you give me any pointers?

Best I can suggest is looking around the raspberrypi.org forums; there is a company making FXO cards for example, which may be the kind of thing you want. You can run Asterisk pbx and do VOIP stuff with a Pi and a suitable modem-thingy. 
https://www.raspberrypi.org/forums/viewtopic.php?f=45&t=86601 might be helpful.

tim
--
tim Rowledge; tim at rowledge.org; http://www.rowledge.org/tim
Strange OpCodes: FSM: Fold, Spindle and Mutilate