No, you are not. You can use almost any mobile network that has a signal in your area, with the selection of network being made via the commercial contract and the physical SIM installation. In fact, there is nothing technically preventing you having multiple concurrent connections all working out of the same box. If you have 8 GSM modules, for example, you could have 2 using Orange SIMs, 4 using Vodaphone SIMs and 2 using O2 SIMs in the same installation, as long as you can get a signal for each network.

However, as this adds more management complexity, it’s only rarely done. More usually, a single network is selected for all GSM modules and the tariffs are reviewed annually. If a change is desirable, then all the connections are moved together to the new network.

GSM Gateways are available in quite a few flavours, so you can be almost guaranteed a connection. Normal (analogue) and ISDN2/BRI - ISDN30/PRI (digital) trunk lines can be connected for mobile voice and mobile data calls. Euro-ISDN signalling methods (Q.SIG and Q.931) are supported.

You will need one GSM module per simultaneous office-to-mobile call. Therefore five simultaneous calls require five GSM modules. If you have fewer GSM modules the PBX will send the ‘overflow’ calls to other trunk lines. You will want to minimise this, as it wastes money – but at the same time you want to avoid spending on extra GSM modules that won’t be fully utilised.

A quick rule of thumb is that most installations need one GSM module for every 4,000 minutes a month spent on office-to-mobile calls. For example, a business making 14,000 minutes of such calls each month would need 4 channels – 3 will cover the 12,000 minutes per month, and the last one would cater for the rest and allow a bit for peak loading.

Actual sizing will depend on the profile of your call pattern: during peak times you may require more GSM modules. During the first month any significant overflow can be identified, and if more capacity is required then more GSM modules can be added. Any business can start saving money now and upgrade the gateway capacity to continue saving as the volume of fixed to mobile calls increases.

The Gateways support both Calling Line Identity (CLI) presentation and restriction. If CLI visibility is enabled the called mobile may attempt to return a call. This can be diverted by the mobile network operator to your main switchboard number if required.

It’s all very well having wonderful equipment, but proper management tools are essential to keep it adding maximum value to the business.

The smallest gateways don’t have any management features, as they typically only handle one outgoing line so management data on call volumes can be obtained from the phone bill.

The larger GSM Gateways such as ‘StarGate’ and ‘BlueStar’ provide statistics reports to check capacity and identify when calls are overflowing to other lines. These gateways can also collect Call Detail Records (CDRs) with information on each call including date, time, number called and call duration. These management features enable you to monitor the gateway performance.

GSM Gateways are highly reliable devices. If a critical gateway failure should occur, simply unplug it and calls will continue to connect over other lines. Because the Telephone System is programmed for this eventuality your telephone service is not affected.

However, in order to ensure that all possible risks are covered, Packet Media Ltd support and maintain the equipment under a maintenance contract. If anything does fail, the fault is diagnosed and repaired quickly.

The gateways installed and maintained by Packet Media are fit for purpose. You have peace of mind that any gateway failure will not affect your ability to make and receive telephone calls. Packet Media are always on hand to give support and visit to site if required.

In fact, the presence of a GSM gateway can actually increase the resilience of your telephone service. If for any reason your fixed lines go down, the gateway is still available. Some minor adjustments to the routing logic in your phone system can route all calls through the gateway, not just those made to mobile devices. We have had customers in just this situation, who have been very glad of having this alternative telephone channel in an emergency.