The wireless modem/phone jack idea is a great one, but it rarely works the way it is intended.  Whether it's interference from other electronics, old house wiring, or any number of things, it tends to have a poor signal resulting in a bad connection.  If you're using this for either a modem, security system that requires a phone line, or a telephone jack, it's likely not going to give you the results you want.  My recommendation would be to go ahead and have a phone drop and jack installed and call it a day.  It may be a more expensive option, but it's by far the best one.