I would like to embed a simple mobile modem in my laboratory device. The capability is not really important - I want to be able to send small amounts of data and have no hard requirements on transfer speed or latency. That means that slow data is OK, text message is OK and even manual modulation over a voice line is OK.
Assume that I live in an area with generous availability to carriers. If you know of a modem that is applicable to only a part of the world, please give that as an answer with that information. If you know of a modem capable of operating anywhere, all the better.
The capability of the modem is not really a concern as much as availability (to consumers), size and price, so GSM, 3G or LTE (even NMT!) matter a lot less than whether I can get my hands on one for a reasonable price and put it in a small shell. This means I, as an individual, want to buy typically one modem at a time.
What brands, vendors and retailers can I choose from? Are there any caveats I should be aware of?