Yes, when there is a data connection working, online SMS services are great.
Sounds interesting! GSM-SMS is great for putting in a 3rd party SIM and just SMS the APN to the device. Our partners are used to that on another product. Or getting a status from a device that lost data connection.
BTW, I found a public example of network time-outs for TCP and UDP that might be interesting for others:
But the tcp vs udp point seems moot after reading these two threads, indicating that TCP is not a viable option, and may be removed anytime soon:
https://community.particle.io/t/electron-tcp-firmware/21078
https://community.particle.io/t/electron-tcp-callfunction/20935
So, it is best to stay away from TCP, and just real life test, what the data cost will be with a 3rd party SIM, for when coverage demands it.