Cheapest way to go would probably be a 551 KSU with a ring generator. You'll also need some 25 pair cable with a female amp/champ connector. If only one line you really wouldn't need the ring generator.
Visit Atcom to get started with your new business VoIP phone system ASAP
Turn up is quick, painless, and can often be done same day.
Let us show you how to do VoIP right, resulting in crystal clear call quality and easy-to-use features that make everyone happy!
Proudly serving Canada from coast to coast.