Ok, now I understand… But I wonder who agreed on doing this. It is amazingly stupid to force a call drop at country border. I doubt the subscriber are happy about this :)) If the call was started in one PLMN, then you might as well finish it over there… It is not roaming !
It will also impact the cell coverage in other directions too. If the BTS is at 500m from country border, then the coverage of the cells is limited to 500m, in every direction.
And what about inter PLMN HO ? Wouldn’t it be a cleaner solution ?