In article om, JF
Mezei wrote:

You cannot disable voice/SMS roaming.

sure you can. just turn off cellular entirely.

What you can do however if you wish to be wi-fi only is to ask for a
disabled AT&T SIM cards (or one that was never activated). This way, you
can be sure AT&T cannot bill you when your phone is on in the UK since
AT&T will tell the local wireless company it does not accept the charges
for that unactivated SIM card).

no need for a disabled sim. just remove the existing sim.

however, that won't work for verizon or sprint, which don't use sims
for 3g (they do for 4g). there's nothing to remove. although there's no
cdma, it might still connect on lte, depending on what bands are in
use.

put it in airplane mode and turn on wifi to be safe if the sim can't be
removed.