I thought Blackberry had their own servers and transmission lines. The was why their mail was more “secure” compared to other providers.
Remember when the Islamists were shooting up folks in that 6 star India hotel?? The Islamist were using Blackberries, and LE could not look into their communications
I don’t think that is quite how that works, but if they have contracts with the US government, then they are subject to congressional oversight. also the BB are connected via a service provider such as verison, AT&T, etc... and they also backup data a long time, you know that the NSA has this data.