Agree. I do a lot of travel and in 3rd-world countries it is quite common to get 2g spam, it's really unacceptable that Apple doesn't offer a way to turn off 2g short of lockdown mode.
Are you sure it's not sourced from the visited network? In that case, 3G or beyond wouldn't help you, as mutual authentication does not imply end-to-end authentication of all traffic between you and your home provider.