Bit late
Wish they'd mentioned this before we went an implemented an SMS based emergency notification system, in conjunction with th service provider, who can adjust the priority based on the message source (i.e. give US priority when we need) several years ago. We thought it had been working perfectly this last five years but apparantly not. We do have an entirely separate backup system consisting of receiving a pager notification - over a dedicated network - and then using Tetra radios to contact control but it has, thus far, not been needed.