Texas

Colorado River
FHU 30/50 amp ($3 per night for 50 amp), $5 UPS/FedEx, No USPS, local (Columbus) post office does general delivery.
 * Verizon is decent.
 * AT&T good up closer to the Ranger Station, okay down by river.
 * T-Mobile is good down by the river.
 * Sprint ?
 * Parkwide WiFi is being installed in December 2018, I assume it will be a paid service.

Lake Conroe
FHU 30/50 amp ($3 per night for 50 amp), $5 UPS/FedEx,.
 * Verizon is decent.
 * AT&T is good
 * T-Mobile is good
 * Sprint ?

Lake Tawakoni
FHU. March 2018 in Section I. AT&T (56ms, down 11.33mbps, up 20.20 mbps), Verizon (24ms, 44.10 download, 12.45 upload).

Lake Texoma
Mostly FHU 30 and 50A ($3 per night), Verizon (26.84 download, 3.20 upload) AT&T (6.19 download, 5.78 upload) Sprint (0.35 download, 0.26 upload) T-Mobile (11.49 download, 0.55 upload). $2 UPS/FedEx, no USPS.

Lake Whitney
FHU 30/50 amp ($3 per night for 50 amp), $5 UPS/FedEx, No USPS
 * Verizon is very good (testing in B section)
 * AT&T very slow, but works in B section. There are reports it's better down by the lake.
 * T-Mobile is okay up by the entrance, but non-existent in B section
 * Sprint ?

Medina Lake
Some FHU 30/50 amp ($3 per night for 50 amp), $5 UPS/FedEx, No USPS, local post office (Pipe Creek) does general delivery.
 * Verizon is decent. Feb 2018 Verizon (7.25 download, 2.27 upload)
 * AT&T is better up closer to the entrance, but good down by the lake as well.
 * T-Mobile is better up closer to the entrance, but good down by the lake as well.
 * Sprint works