Originally the SMS data was carried in the control channel and not a data channel for 2g phones. The control channel has more resilient error control as it is the link between the handset and network. This means that SMS (on 2g) stands a much greater chance of making the trip than any other comms to the phone.
3g and LTE/4g phones have very much higher bit rates which is why they can do multi mega bps comms. But that speed comes at the expense of power used and bit error rate. Or if you want to go very fast you need to use more power and you need a very good signal to noise ratio between phone and tower. As the signal to noise drops then so does the speed.
I haven’t looked into the specs as I used to do with 2g, but the basic signalling between the phone and tower takes place at a low rate with a strong degree of protection against errors. This is so the network can tell your phone to receive a call or message. When a voice call occurs your phone ramps up the data rate. For internet access, 3g/LTE phones try to establish the highest data rate and the signal to noise ration has to be very good for high rates.
It’s because the phones try to establish high bit rate links that internet access “in the wild” can be difficult but as SMS is carried at slower rates it will work. Of course if you can get a data connection working you’d be silly not to use it.
On top of all of the modulation rate info there is frequency selection. Frequency bands exist at 800MHz (newish) 900MHZ (very old), 1800MHZ(old) 1900MHZ(old), 2100MHZ(quite old) 2600MHZ(new). The higher frequency bands have more BW so you get more channels and more data. The low frequency bands over better distance and work much better in buildings.
So you have to consider absolute coverage of the network, the frequency band the network has where you are, whether your network forces you to use the higher frequencies first, the actual mode your phone is in 2g.3g,4g etc. and it all gets awfully complex very quickly. So in my case I pull out my phone on a summit and look at the signal strength meter and try to load the spots page. If it doesn’t do that quickly then I’ll use SMS if I need to self spot. I can’t be bothered flipping phone options to see if I can make the data link better. If it works out of the pocket, good. Otherwise I’ll stick with SMS.