How does a GSM gateway work?
The GSM gateway contains one or more SIM cards. A call from the company's PBX arrives at the gateway, which routes it through a mobile network using a SIM card. As a result, calls to mobile numbers are billed as outgoing calls under a mobile tariff, not as calls from a landline to a mobile network.
Physically, the device is connected to a PBX (private branch exchange) via an analogue or SIP (Session Initiation Protocol) interface. The gateway functions as a standard telephone line to the exchange but uses a mobile connection for outgoing calls.
The same principle works in reverse, incoming calls to the SIM card in the gateway can be routed directly to the central station and then to a specific branch.
When did companies use GSM gateways and when do they make sense today?
The main reason for installing the GSM gateway was cost savings: calls from mobile to mobile were historically significantly cheaper than from a landline. With the gradual change in operators' tariff structures, especially including calls to mobile networks in flat-rate plans, this reason has largely disappeared.
Today, GSM gateways make sense in these situations:
- In locations without available internet connection where VoIP cannot be operated.
- For backup communication in case of an internet outage.
- For specific SIM cards with favourable roaming when working abroad.
- In environments where a transition to VoIP is prevented by internal regulations or older infrastructure.
GSM gateway versus cloud-based PBX
A modern cloud-based PBX does not require a GSM gateway as a separate device. Instead, it uses a SIP trunk from an operator whose price list includes calls to mobile networks. For mobile employees, softphone applications (software phones) or FMC (Fixed-Mobile Convergence, integration of fixed and mobile networks) are used.
On virtualni-ustredna.cz, mobile accessibility is handled via a smartphone app, so employees can make calls from their mobiles using the company number without needing a physical GSM gateway.
Frequently Asked Questions
Is a GSM gateway the same as a femtocell (operator microcell)?
No. A GSM gateway is an active device with its own SIM cards that bridges the PBX and the mobile network. A femtocell (microcell) is an operator's device that extends mobile network coverage inside buildings. It operates on a different principle and serves a different purpose.
Can a GSM gateway be connected to a cloud central station?
Yes, if the GSM gateway supports the SIP protocol, it can be connected as a trunk to the cloud PBX. Older analog gateways can be connected via an ATA adapter. In practice, however, this scenario is becoming less cost-effective; a direct SIP trunk from the operator is usually more advantageous.
What are the risks of operating a GSM gateway?
The main risks are: the need for regular checks of SIM card status and signal, limited capacity (the number of simultaneous calls corresponds to the number of SIM cards), physical wear of the equipment, and dependence on mobile operator coverage.