We want to inform you that some smartphone models are not fully compatible with all network bands in every country.
Indeed French Carriers are using 5 bands for LTE, and depending on their origins some smartphones are not covering all these bands.
For example for iPhone XS and above, phones from US/Canada/Hong Kong and China are not covering band 28. This can lead to network reception issues depending on which band the antenna the client is pinging-in is using.
Please note that those references of smartphone cannot be sold in a country if every band is not covered. All details by countries and smartphones here.