99% of consumers do not understand te CDMA TDMA GSM Analog giberish. Keep it simple stupid is my solution. If you can't make a call it is considered a "dead zone" and should be submitted to our database. Gaps in the national cellular coverage exist because the CDMA/TDMA/GSM providers to not cover the whole nation. The only thing still in common with the various cellular carriers is the original analog system. As you move around the country you should get service on your digital service or switch to analog service, if your digital service is not available. Sometimes you may pay extra to make an analog call (aka roaming), BUT at least you can make a call in an emergency situation. Most newer cellular phones support both digital and analog frequencies, so if your digital services is not available the phone should switch to analog services.