One of the main reason why M2M applications are using SMS together with GPRS is indeed that network initiated GPRS sessions are usually not supported by GPRS networks. Therefore servers need a way to ask the unit to go into a GPRS session and this is usually done via SMS or CSD. Other cellular technologies like CDMA do support network initiated and do not need SMS or CSD.
One interesting downlink traffic is firmware update, very important to implement for M2M applications.
As noted, SMS is the primary driver for M2M devices being Class B. In addition to providing the shoulder tap functionality, operators use special SMS messages (SIM OTAs) for managing the content on and configuration of the SIM. Since SMS over GPRS is not widely supported, SMS over CS is required.
Here is a device that is intended only for a GPRS network. It is configured over a serial connection. You can use it with M2M RTU Center Software on a PC and you can access serial devices at remote locations with it.
GT-540P: $679.00 Wireless Intelligent GPRS Remote Terminal Unit with GPS and 2G micro SD card for remote monitoring applications. Ideal for Vehicle Tracking. Has 6 DI, 2 DO, and 1 AI
M2M RTU Center: Free M2M RTU Series Management Software
ICP DAS USA, Inc.
1-310-517-9888 ext 105
We provide free technical support.