there should be a timer in the phone that forces the MS to select its own HOME PLMN after few minutes. I forgot the value of this timer… 4 minutes ? 30 minutes ?
It is hardcoded in the phone…
A workaround would be to set the phone to “manual network selection”. When HPLMN is lost, the MS is “out of coverage”. Connectivity will come back when MS is back in HPLMN’s coverage.
In limited service, MS can send Emergency Calls only. Cannot receive, cannot make “normal” calls.
(ps: if you search in this forum, you’ll see a post about this topic where I wrote the duration of the timer..)