An ATA or Analog Terminal Adapter can connect to a voip line and give you a dial tone that acts just like a regular phone line.
You could get one connected through any variety of voip services.
The biggest problem would be that modems do not work well over voip lines. Your standard dial up type of modem uses an audio type of signal, which is really analog sound, IP signals are broken up into packets, and if any are lost or mixed up, they can be resent. Your voice can miss a syllable and I'll still understand you, and a website can take an extra moment to load, but when the modem sounds are interupted, then the modems get really lost and often disconnect.
That said, it can work, and better if you are using a lower speed, such as 9600.
I just tried to do some remote work via modem over a voip line, it took me at least 10 attempts. I was able to connect, but was consistently disconnected before I could finally hold the connection long enough to make the changes I was doing.
Why is there no phone line available for the computer? Is it just that there is nothing available in that particular room?
You will still need to pay monthly for a service to provide the number and connection you need.