There are several types of forwarding you can use including most cell phones
Overflow Calls: You can setup with your local telephone company to forward you calls to the answering service only at certain times. See below "No Answer Call Forward" & Busy Call Forward"
Telephone Branching: You can setup with your local telephone provider to have you phones permanently forwarded to the answering service. Use this option if you never want to answer your phones yourself.
Remote Forwarding: This is a great option if you want to forward your phones to the answering service no matter where you are. This option is setup with your local telephone provider.
No Answer Call Forwarding: This option is also setup with your local telephone provider. This is great for the "one man office". You tell your provider how many rings, 2, 3 or 4 to ring to you. If you do not pickup, it automatically rolls to the answering service.
Busy Call Forward: Also setup with your local telephone provider. If your caller gets a busy signal, he may go on to another business that someone does answer. To prevent this problem, use busy call forward. The line will go to the answering service rather then your caller getting a busy signal.