Yes, when crossing a border between two countries covered by the 1NCE footprint, the 1NCE SIM card ensures seamless connectivity. However, this only applies to the connectivity standards 2G and 3G. NB-IoT does not support seamless cell handover when switching cells. In this case, the connection is lost and has to be re-established. You should also note that NB-IoT is not yet supported in all 1NCE footprint countries.