The BlackBerry phones didn’t operate on pager frequencies did they?

It wouldn't surprise me if the BB push notifications worked over pager frequencies. I can't find anything online about how they actually worked, but the original two-way communications device from RIM was called the "Inter@ctive Pager"[0]. If I were to guess, I'd say it is possible the push notification went over a pager frequency and included a snippet of the message. The device would then be able to request the full message over the cellular data network. The pager networks of the time were more robust (and travelled longer distances), so the BB would be able to received the notice of a message (and part of the payload) even in a cellular dead-zone.

But, that's just me speculating...

[0] http://www.braddye.com/newsletters/2010/n22jan2010.html

So the first ones used pager networks, the next generation used cellular.

The push service was quite good IMHO. Every carrier that supported BlackBerry Internet Service had a leased line or VPN to the RIM NOCs. The phones would connect to BIS servers at the carrier which then communicated over these backhauls to RIM. Because it was all so deeply integrated in the carriers network (I believe the BIS servers acted as a Gateway GPRS Support Node), the BIS servers knew exactly where on the network each phone was, so they could send essentially a UDP packet directly to the device, which was listening on a particular port. No long standing TCP connections, and of course if the device didn't acknowledge messages, they were queued at RIM for when the device reentered coverage.

Email was provided by a server side process that opened MAPI (the original exchange RPC protocol) connections to exchange mailboxes and asked to be pinged if there were changes in mailboxes. When that happened, the BES server would pull the changes, package them, forward them to the RIM NOC over the proprietary SRP protocol, which would locate the right carrier, send the packet over the backhaul, and then from the carrier it would make its way to the phone.

Source: used to run a BES server

This sounds worse than modern ActiveSync - which Apple introduces support for in 2010 (2009?). You also didn’t have to send all of your email through BlackBerry’s servers.

With ActiveSync, my email will usually reach my phone/cellular watch/iPad before it reaches my computer.

True. The messages were encrypted, but ye if RIM went down, no email for you. Even if your email server was working fine.

Well, it being encrypted doesn’t help when RIM had the encryption keys and would give them up to any government entity.

https://www.schneier.com/blog/archives/2008/05/blackberry_gi...

https://www.engadget.com/2016/04/18/blackberry-ceo-wont-say-...

So that applied to consumer users. When connecting via BES, the connection was end to end encrypted, RIM never had the keys.