In general, I don't think there are much. However, they are configured differently. Both your CPE and your service provider have to support the appropriate protocol whether it's data or voice. I do know that there are extra charges when associating PSTN connections to your PRIs.
If I am not mistaken, you can now run both PSTN and data over the same PRIs if your equipment supports it and your provider offer this solution.
So, if your question is "Can I plug my voice router into my data T1 port" or vice-versa, the answer is no. I asked this to my provider. ;)
I'm not a T1/PRI expert, but that is my experience after talking with some people.
By the by, the sharing can also be dynamic, for example, if you have a WAN link over fibre and one T1/PRI for voice, you can effectively program your voicegateway to split the T1 in half (or use one of many) to be used for data in the even of WAN link failure.
