For the best possible Data speeds over a phone line, here are the things that your Phone Tekkie should look at. Print this and have your circuit tested and insert the values below:
AC Voltage:
Ring Voltage:
DC Voltage:
Stress Test: Should be 0 to 20 db. 34 db is unsat
Noise: 0 to 2 is acceptable
Power Influence: 60 to 80. 80 is better.
Loop Current: Should be 23 ma or higher