You have several things to consider here:<p>1) Making sure the phone matches the bands offered by his mobile provider in his area. For example, T-Mobile has greatly expanded their band 12 coverage over the past year, but most mobile phones don&#x27;t have band 12 coverage.<p>2) The actual RF qualities of the radios on the mobile phones.<p>3) Many mobile providers offer Wi-Fi calling, so this can be an alternative in a poorly covered area. However Wi-Fi calling is dependent on device support.<p>4) Many mobile providers offer free or cheap repeaters that connect into your cable modem or DSL routers. These emulate LTE or 3G base stations and can be used to make calls in poorly covered areas. This too works well in homes, and with any devices.