2G only, but disallow 2G rule

The advanced way of setting preferred network type on android is typing this in the dialer: *#*#4636#*#*

It will show a menu with all kinds of options. Lots more than the normal GUI shows.

That’s how I got that, xD. Android doesn’t otherwise list 2G as an option anymore, though it can still display it.

I wish I could deselect 3G however, since that isn’t a thing in my country anymore. (While keeping 2G)

Even more advanced (on MediaTek) stuff is in *#*#3646633#*#*. It’s called engineer mode, and typically gets removed in OS shipped to customers, but some manufacturers just don’t do that (smaller Chinese). There I can even select specific network bands, or even specific cell tower by EARFCN and Cell ID, as well as tinker with settings I rather won’t touch because I don’t understand them. And for example, manual MTU setting can persist a factory reset, so not everything may be resettable.

Even funnier, and probably part of the reason for removal, there’s Tx tests. For WiFi and cellular. Unfortunately, it only works for 4G on my current phone, and it blasts full power no matter the setting. But on my other MTK phone I can select 2G, 3G or 4G, frequency to transmit on, bandwidth, modulation, power level, type of data to transmit and some other settings.
Welp, that one sounds illegal.
I checked it with my SDR, it works. (The lowest power only seems to reach a few cm).
Lastly, based on screenshot found on XDA, some variants allow easily changing IMEI via GUI, or at least using AT commands. Also likely illegal.

I find it very useful for the band selection.