|No problem using the rj12. They are both the same size plug.|
The difference is that the rj12 has 3 pairs (6 wires) and the the rj11 has either 1pr or 2pr (2 or 4 wires). In all cases, the center pair is line 1 the next pair out is line 2 and the last pair (outside wires) is for line 3. dsl only uses pr 1 (center pair), which is the same in both cables.
How to Wire a Phone Jack
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