Glossary

VoIP GSM gateway

A VoIP GSM gateway is a device with SIM cards that connects a contact center's IP telephony to the mobile network. A call from the system goes out through one of the gateway's SIM cards, and the customer sees a regular mobile number. Companies use a gateway when calling mobile phones from SIM cards is cheaper or more convenient than going through a SIP trunk.

Why it mattersYou can call mobile phones from regular SIM cards – sometimes cheaper than through a SIP trunk.

Also called: GSM gateway, VoIP-GSM gateway, Cellular gateway

How it works

The gateway connects to the PBX or contact center platform over IP, usually via SIP
You insert SIM cards from mobile carriers – typically 1 to 32, one per port
Outbound calls go out through a free SIM card, and the gateway passes calls to a SIM card's number into the system
One SIM card handles one call: a gateway with 8 SIM cards supports 8 simultaneous calls

Limits

Limitations

Mobile carriers restrict high-volume calling from regular SIM cards and may block them. For outbound campaigns, you need a plan that allows it
To add lines, you have to buy more SIM cards, and sometimes another gateway
Call quality depends on the cell signal where the gateway is installed

Comparison

GSM gateway or SIP trunk

GSM gatewayYour own SIM cards and mobile numbers; as many simultaneous calls as you have SIM cards.

SIP trunkCarrier lines over the internet; you change the number of simultaneous calls by asking the carrier, with no hardware.

In CONTACT.WORK

How it works in CONTACT.WORK

The CONTACT.WORK platform works with both SIP trunks and VoIP GSM gateways, and you can connect both at once. For auto dialer campaigns, we size the lines to the number of simultaneous calls you need.