Installing a new phone jack. Which wiring to use for only 6ft? Help!

Hi.

Im installing a new phone jack that is only using a 6ft cable from my telephone interface box to the jack im installing in the wall. (the spot is right on the other side of the wall).

What cable should I use? Cat 5/6? Or can i just use a regular telephone cable... I originally planned to just use a regular phone line and just connect green/red, but when I looked at the wires they were kind of thin, and im not sure how theyll do outside.

The only use for this jack is a dsl modem. Its going to be doing 3Mbps and I want the fastest speed possible.

Theres going to be 6ft from telephone interface box to the jack, then a 25ft regular telephone cable from the jack to the modem. Is 25ft too long?

Please help!

Thanks!
Greg