I use TMobile, my husband uses Verizon, and my mom has At&t. We all have poor/no reception inside the rooms at CSR. We always have to go outside or sit right next to the window to use our phones.
My elderly mom is a very brittle diabetic who takes a short acting insulin after each meal and a long acting insulin every night around 10:00pm CT. When I was at CSR Nov 26th-Dec 4th, I had to call her every night about 11:00pm ET (10:00pm CT). I was in Cabanas 8B facing the parking lot. There was no service right outside my room, so had to get out of bed, then get dressed every night, and walk around by the stairwell or the quiet pool in order to get a signal to call her to remind her to take her insulin and make sure she was OK.

Usually I can just stick the phone over by the window and sit on one of the ottoman's or else just step right outside the door to make calls, but two weeks ago I had to wander around toward the lake side of the resort in order to make cell phone calls. I had perfect reception on that side of the building though.