Telephone Line Specifications
This reference is an old "e mail". The link is at the bottom of the document.
There is some speculation if all the listed values are 100% correct. Minimum line current is listed at 20 mA and most people will tell you the value is a bit higher then that, around 23 mA. The minimum voltage is listed as 8.6 Volts, this value is in question, some think it should be 48.6. Also the "phone resistance" is too high, in common practice 200 Ohms is a good value to use. So, read it with a questioning eye.
This document is in MS Word. Click HERE to download it.