Hi, yes you can run both on the same line, you say voip line, is this a phone POTS line from the ATA or are you putting a IP phone at this location.

I am assuming you want to run a normal pots/phone line back to the VOIP ATA port, then its fine to run a single cat5 run, terminate it fully (all 4pairs) and use a line splitter at each end to get a data and phone circuit (product C-RJ45LT4) as linked below

http://www.cablesdirect.co.nz/catalog/entry?entry=334

Only limitation of using above splitters (or by doing it hardwired in the socket which I recommend you dont) is that you can only do 100Mb/s FastEthernet never GigE, as GigE uses all 4pairs.

Cyril