Earlier quoted context omitted.
Blackberry was always the weird one out that effectively depended on special service from your provider combined with special tariffs for using them. This is a legacy from when they were explicitly enterprise devices and you couldn't exactly buy them normally. Similarly, the core functionality of the original BB - email - is no longer supported (though you can probably run it still) because the special server softwar…
Even today some apps like Outlook for Android use Microsoft servers for proxyiing email service and don't connect directly to the mail servers from the phone.
In case of BB, it was literally a special protocol running on the telco network, combined with the special rates, to enable live email access when GPRS was, well, new and mostly unavailable.