You could report it with your phone carrier, and have your mom do the same. Carriers keep something called CDRs that will have some level of debugging informati

You could report it with your phone carrier, and have your mom do the same. Carriers keep something called CDRs that will have some level of debugging information associated with it. They might turn up something obvious right away. The truth is, they're not going to do anything about it unless it's recurring. And then, you'd better hope it is reproducible, or the techs will keep closing the tickets and moving on. I've done a lot of telecom work for intermediate sized carriers. I've dredged through many gee-bees (that's gigabytes, folks) of SIP logs, cross reference my ass off, set up intermediate traces with IXCs, you name it, all in search of answers to problems just like the one you described. The problem is that the system doesn't stay the same for long. The telephone network in the US is more varied and complex than the Internet, because it has an unholy mix of legacy and new technologies glued together in ways that will make you lose sleep at night. At some point, you develop an appreciation for the fact that it works at all.