It looks like this account is still using a 2G communication module. The signal history is showing a sharp decline in signal as of late. The 2G cellular infrastructure is in the process of transition, and certain areas may be affected sooner than later.
The majority of recent signal strength reports show single digit signal. (11 is what we recommend as a minimum.)
The best way (and really only way) to resolve this is to replace your communication module with a 3G module. You will want to check to see if you need to update firmware in order to use a newer module.
3G AT&T require 1.9.6 or higher. 3G Verizon require 1.9.5 or higher.