I haven't tried it myself, but a null modem cable (full handshaking preferrably) between the 7400B and a modem should work.
You may have to strap leads together to make it fully functional. Like I said, I haven't tried it.
As always, be EXTREMELY careful putting a modem on your switch. They are easy to find for anyone looking for them, and you only have userid/password protection.
And if you use PC Anywhere, please enable the security functions (V.8 and newer make this easier). Do things like disabling file transfer (you shouldn't need it, and if you do, you can turn it on each time you need it).
mgs