How many of the phones and devices are connected to the line? All of them? You may have too many devices on the circuit. Every device pulls a bit of current from the line. If too much current is being pulled, too many devices, some of them may not get enough current to work, won't ring or get a dial tone. If it all worked before DSL, could be the DSL filters themselves are pulling enough current to make the difference between the phones working and not.

I have a 4 phone system. We first had a system with 2 phones on it. Then we bought a system with an answering machine so we now have the answering machine base telephone plugged into the wall, and the other 3 phones work off of it wirelessly.
AR_D

Had the same problem then Verizon came out and removed all the individual filters and put in one main filter in the service box outside. Haven't had a problem since and the DSL works much faster.