Yes you can use the same cable to supply data and voice.
The best you can get out of the data is 100meg as 1000 meg uses all 4 pairs.
You will use the centre pair as the voice and the 2nd and 3rd pair for data.
4th pair will remian unused.
How is it wired at the point and the other end.
If he has terminated the end in the room on one outlet then you will either have to turn it into a double point or invest in some cat 5 splitters.
At the remote end or Patch Panel or wiring closet you will require to do the same as the room end. You will have to split it into the device you intend to use it for.
At the Head end a better solution if it has not been terminated would be 110 or krone highband. If it is on a patch panel then it is going to be messy.
My suggestion is ask him to rectify the wiring as per your requirements, if it is not met them make a complaint to the Communications body.
Using Data and Voice on the same cable is not of real concern as the attenuation and NEXT and FEXT will not really come into it as the maximum speed you will be running is 100meg, also in a home the max distance would probably be around 40m unless you live in a mansion.
A cat 5 splitter is around about $10 baring in mind for every cable you will require 2 if it is done as a patch panel
A good product to work with where the re-cabling is not an issue is the AMP ACO outlet, it offers flexibilty and changes to the outlet via plug in adapters.
Hope that helps :)