I think that trying it that way will not work period.
Nice idea though; dont get me wrong.
I think your problem is cross-talk between the network and the phone lines. The phone lines run at say 7V where networks run at less than 5V. The phone line just sitting next to the lines will cause so much noise in the network lines that the NICs just give up.
I am basing this on the fact that when I first started making CAT5 cables, I was dumb and made all the lines straight across (AKA 1->1, 2->2, 3->3, 4->4, 5->5, etc). That would work for runs 20 feet or less. After that, the cross-talk just from having the Rx lines on different twisted pairs would cause the link to fail.
I could be wrong however. I hope that some one can prove me wrong acutally
Try isolating each side first and then testing it. Such as, disconnect the phone lines in the CAT5 and just run network and see what happens. As long as you have pins 1,2,3,& 6 running correctly, you sould get a link. Otherwise you might have something wrong with the CAT 5 cable.
Justa suggestion.
Good luck though