If you are looking for a third-party solution that is available immediately, the Microduino stackable system has a GSM/GPRS unit. It is designed to be stacked directly onto one of their Microduino "core" controller units and can be found here:
https://wiki.microduino.cc/index.php/Microduino-GPRS/GSMHowever, it is important to note that this is a 2G (not a 3G) cellular devices. If this product is intended to be used in the United States *AND* it is intended to be in use beyond 2016, please be sure to review the following announcement from AT&T regarding their sunset of 2G coverage to ensure the cellular module will work for your intended lifecycle:
https://www.business.att.com/content/other/2G-Sunset-FAQ_2016.pdfAnother product line you may want to consider for cellular communication is the ReliaCELL USB-connected cellular modems available from Eurotech:
https://www.eurotech.com/DLA/datasheets/Products_Eurotech/ReliaCELL10-20_sf.pdfYou have a number of ordering options available to you with the ReliaCELL:
* 2G (1xRTT) for CDMA-based carriers who will support 2G for a number of years (i.e.: Sprint in the USA)
* 2G/3G - I have not heard any announcements about sunsetting 3G anytime soon (typically 3G units will still cost less than LTE for a while)
* LTE-Only - If you require a LONG product lifecycle and the LTE coverage is sufficient in your intended deployment geographies. LTE is not supported for ALL carriers, and will likely come at a premium.
* Global connectivity options
NOTE: While the ReliaCELL is not in a stackable form factor as small as the Tinyduino/Microduino form factors, it can be remotely mounted where the cellular signal can be best received (for example, the ReliaCELL can be mounted OUTSIDE of the enclosure, or even mounted many feet away (since it connects via USB)). Depending upon your enclosure material, you may find numerous benefits to this approach.
Essentially, you can treat the ReliaCELL as if it were a remote antenna (except in this case, you do not have to deal signal loss created by long coax runs (it connects via USB can run for several feet - and even be expanded with active repeaters, if needed to get outside of a building, a vehicle, etc.). The antennae mount directly to the ReliaCELL and it can be mounted outside due to its extended temperature range.
One key consideration: The Eurotech ReliaCELLs are already certified with various carriers and will not require going through the lengthy and expensive carrier certification process that some of the carriers require when modules are embedded into products that connect to their cellular network. The ReliaCELL approach gets you to market immediately (no additional carrier certification needed).
Anyway, I have probably given you a bit more info than you wanted.
However, having previously worked at a cellular carrier here in the USA, I thought I would try to save you some of the grief that developers typically encounter which ends up derailing their development schedule.
Hope this helped...
John
