Line: A single Phone line or PBX Extension
OGM: Outgoing message
This includes any message, menu or interactive feature callers can be presented with during a call. 1 OGM basically means the software can only be used in its most basic form, a simple answering machine.
Outbound Call: IVM can be used to make outbound calls for several reasons:
- Forwarding / transferring calls
- Telemarketing
- Reminders
- Call-back service
etc.
You are right in that it is not a common feature for home use.