I use Verizon MiFi with Jetpack and they do advise at 50%, 75% and 90%. You can call or go online and increase your service at any time, then reset at the beginning of the next month. I've been through West Texas, remote as it is, and have maintained my 3G coverage in the past. I'll be going again shortly with the Jetpack and don't anticipate problems. AT&T has MANY spots of no coverage where Verizon just drops to 3G (with little drop off in speed) and keeps going.