When I worked in a wireless repair shop in early 2000's, we handled the local FBI field office account. Field agents would come in and I'd chat them up as they sat and waited for me to fix their phones.

This was also around the time remote meth labs were getting really common out in rural areas. Multiple agents were talking about how frustrated they were with getting access to burner phones since most of the companies were resellers. They said by the time they got a warrant to start recording the devices, they were already dead.

I guess the bad guys knew their burner phones were only good for about two to three months tops. That was usually the timeframe from when the FBI got a read on a line, saw a judge and got the warrant processed, to contacting the carrier and getting access.

Sounds like whatever was hampering them in the past has been fixed.