In 5 years time rural coverage isn't going to be a big issue on ANY network as AMPS will be dead. Right now most rural AMPS networks (that partner with the majors for roaming) are overlaying CDMA800 and GSM850 onto their AMP (in some cases limited TDMA networks).

These rural operators are going with BOTH CDMA and GSM overlays to ensure they can capture ALL roaming traffic (we're talking about places in the US where there is NO need for competition, e.g. VERY sparse local populations)