It is possible to make cellular phone calls in areas with limited coverage, but call quality may be diminished, and calls may not be possible if the load on the network is high. Switching to a different cellular network standard can sometimes improve signal strength in low-coverage areas.
Many modern cell phones support several cellular network standards for transmitting voice and data such as the 3G and 4G protocols. Not all carriers have equally good coverage for both 3G and 4G transmissions in all areas. For example, 4G coverage may be limited in an area, but 3G coverage may be good in that same area, so switching to 3G can potentially enable better call quality there.