GSM was developed to support packet switched data communications (GPRS) but a quite well hidden secret is that GSM also supports the circuit switched data communications (CSD) used in the traditional fixed phone networks (PSTN). CSD made it possible to move terminals from PSTN to GSM-networks which still is an attractive approach in networks where CSD is enabled. Typical usage has been encrypted phones and mobile fax. Still today this is an attractive way to move fixed terminals to a mobile network to save money, add flexibility, enable wireless offices or to enable fixed line operators to remove parts of PSTN that never can be upgraded to broadband and/or don’t have subscribers enough to carry the infrastructure cost. There is an important difference between moving an existing PSTN terminal to a mobile network and to replace an existing PSTN terminal with an IP-enabled mobile terminal. Reasons for moving terminals include taking advantage of made investments in products and education, a desire to make changes step by step and last but not least that some applications like fax is technically very difficult if not impossible to do over a packet switched network (like GPRS). On top of technical arguments are things like the need to call a place and not an individual. Mobile phones are personal and fixed phones often shared.
The PSTN networks are on their way to be replaced by mobile networks but the situation differs a lot from country to country. In Sweden TeliaSonera has started to take down PSTN in rural parts of the country replacing the subscriptions with mobile alternatives. At the same time subscribers leave their fixed phone subscriptions behind and it was recently proposed that the concept of area codes are taken away to mirror the fact that the fixed phone is going away. The number of fixed line subscribers in Sweden are 2,5 million, almost half of ten years ago, compared to 13 million mobile subscribers. The concept of mobile one phone offices once invented by Spring Mobil in Sweden is now very popular in Northern Europe. By moving the switch to the network and removing the fixed phone infrastructure companies save a lot of cost and increase accessibility and flexibility. But the fixed infrastructure was often used also for other things that has to be taken care of including fax, door opening systems, conference phones, alarms and franking machines. I think the one phone offices will continue to spread and this will be the single biggest market for moving terminals from PSTN to mobile networks over the next couple of years. But it has to be underlined that it is not a simple thing to do since both fixed and mobile networks behave differently and many of the fixed network devices use odd protocols for communication. Most difficult of all is fax since it uses a very sensitive protocol.
In developing countries we often see fixed networks with limited coverage and mobile networks gaining momentum due to speed and cost of deployment. Most of these networks are still 2G and in combination with extensive use of paper mobile fax is a popular CSD application. But generally speaking I think GPRS will be the predominant connectivity method for M2M applications in developing countries many years ahead.
Moving devices from PSTN to mobile networks is an important part of the M2M industry. Since it seems like nobody has good enough data on the size of the M2M over PST market I would appreciate any data you could share with me on connected machines to PSTN and I hope one day to be able to share a decent overview helping us all to address this part of the M2M market which I often refer to as the narrow band data opportunity.