Which hardware can we use to get mobile connectivity per 2G/3G/4G for our devices?

1. Huawei E182E/E173 USB dongles

So I looked at these first for 3G and below connectivity. They're fairly low-cost e.g. I got one for £30, but they're also fairly icky to use! The Rasp Pi doesn't like powering them and you tend to need a USB hub instead; and they keep getting treated as USB storage instead of a modem. Some of the issues and solutions are outlined here: https://flyingcarsandstuff.com/2014/11/reliable-3g-connections-with-huawei-e182ee173s-on-raspberry-pi/ // I'll make a post about it myself later, as this will be one of the possible connectivity solutions we'll be using.

2. Adafruit FONA 808 - Mini Cellular GSM + GPS Breakout

Ok, this is great and it's only ~£50. But I can't get a 2G SIM in the UK for it! We can send out SMS with it, and we can send/receive GPRS data (TCP/IP, HTTP, etc.), has GPS. Thus can send our alert messages to either twitter, or a server. It's also voice, so perhaps could send out audio files to voice as alert warning method? I hadn't considered that until now. Anyway, it'll be great in places with a 2G network.

3.  SIM5215E 3G/GPRS shield over Arduino and Raspberry Pi

So with this we've got SMS, voice (again possible to send audio files like this?), GPRS, and 3G. They've got code all ready for FTP/FTPS, HTTP/HTTPS, TCP/UDP! So that's really great! The only problem is that it costs 250 euros! And this SIM5215 doesn't even have GPS. 

Code examples/manual: https://www.cooking-hacks.com/documentation/tutorials/3g-gps-shield-arduino-raspberry-pi-tutorial/

https://www.cooking-hacks.com/3g-gprs-shield-for-raspberry-pi-3g-gps

Frequency coverage:

SIM5215A 

Dual-Band UMTS/HSDPA 850/1900MHz

Quad-Band GSM/GPRS/EDGE 850/900/1800/1900MHz

Output power: UMTS 1900/850: 0.25W

SIM5215E

Dual-Band UMTS/HSDPA 900/2100MHz

Tri-Band GSM/GPRS/EDGE 850/900/1800MHz

Output power: UMTS 2100/900: 0.25W

I'll need to check these against which we'll have in the countries the system is intended for!

4. Altitude Tech IOT BIT 3G HAT for the Raspberry Pi – UK, EU & Asia region

This one looks promising!  We've got 3G again, and SMS, but we've also got a GPS. And we've got our frequencies in other countries covered. Well hopefully. And this one is a more reasonable £166.66. Note, it uses nanosim.

Info: https://hackaday.io/project/25925-pianywhere-4g-lte-hat-for-the-raspberry-pi and http://www.instructables.com/id/PiAnyWhere-4G-LTE-Hat-for-the-Raspberry-Pi/

5. Adafruit FONA 3G Cellular + GPS

Ok well, it's 3G, voice, SMS, and GPS too. Unfortunately the library is under heavy development - so we would kind be on our own at the moment with this. It's £80. Details here: https://learn.adafruit.com/adafruit-fona-3g-cellular-gps-breakout/overview

SUMMARY

The Altitude Tech one sounded good, but I was a bit put off by lack of code examples, and some negative comments from users re support on instructables.com. And now I've found out there is 60 euros tax on the SIM5215E; this brings it to 350 euros w shipping! That's really too expensive! So I'm a bit stuck! I'll probably try the Adafruit Fona 3G and see how I get one with that for now.