|To answer the question re' the phone line...|
That phone line can be used with any dial up modem - but only one modem a time can be "active".
How to install/connect a usb modem?
Such kit will come with a setup disk and manual (or ought to). Your prime issue though is whether or not they will be compatible with the OS on the computer involved.
A kwik look-see (Google trawl) seems to find some that are OK upto win-7, but no mention of win-8; although a deeper trawl may find them.
edited per trvlr - to correct typos
message edited by trvlr