IP PBX enable you to connect traditional  PSTN to voip device such as IP Phone, mobile SIP Phone,. PC, Gateway.... which means you can save phone cost and diverse your working force around the world.

EX : Your head office has 10 workers, and you have a branch office in other city. You install a small size IP PBX in head office which has 4 PSTN lines for customers to call in. 

The phone is IP Based phone set which connect to local Lan line. The other sales office only put some IP Phone there and register to IP PBX as an extension of head office.

The sales person often  travel to different cities, so they use PC or Mobile phone and make internal calls to office or outside calls to customers occasionally which save them a lot of phone cost.

Part of the IP PBX models:

Models	Mosa4603 plus	Mosa4604 plus
Picture
Analog Ports	˙1 FXO+2 FXS	˙4 FXO ˙4 FXS ˙4FXO+4FXS
SIP ports	˙24 SIP Lines ˙4 SIP Trunks	˙24 SIP Lines ˙4 SIP Trunks
Models	Mosa4608 plus	Mosa4616 plus
Picture
Analog Ports	˙8 FXO ˙8 FXS ˙4FXO+4FXS	˙16 FXO ˙16 FXS ˙8FXO+8FXS
SIP ports	˙48 SIP Lines ˙8 SIP Trunks	˙48 SIP Lines ˙8 SIP Trunks
PBX Functions	Auto-Attendant DISA Network Operator Inbound Call、Outbound Call、Transit Call Call Pickup Call transfer Call Forward Group Ring 3-Way conference Trunk Group Baring Speed Dial ..... CDR Recordings ( Options )