There are three parties involved (besides the network):
A) Push Initiator (PI) (NOT the device, but the push content provider)
B) Push Proxy/Gateway (PPG) (this is BlackBerry's Infrastructure)
C) Push client (BlackBerry device)
An example push message in a confirmed (ie. connection-oriented) manner:
1) The content provider (PI) sends a PAP push request
to the BlackBerry Infrastructure (PPG). This request
includes a list of the subscribed BlackBerry
devices to which the data should be delivered,
as well as the data to be delivered. 2) The BlackBerry Infrastructure returns a response
to the content provider, acknowledging receipt of
the request, and queues the request for delivery. 3) The BlackBerry Infrastructure pushes OTA the data
to the specified BlackBerry devices. This doesn't
have to be only a notification of new content;
I think content (up to 8KB in size) can be pushed. 4) Each BlackBerry device returns a response to
the BlackBerry Infrastructure, acknowledging
receipt of the data. 5) The BlackBerry Infrastructure forwards the
acknowledgement on to the content push initiator. 6) The Read notification is returned to the
BlackBerry Infrastructure.
(One-way push only does steps 1. and 3.)
The push (step 3.) actually works through a Network
Operating Center (NOC). RIM is able to do this because
the BlackBerry device necessarily registers itself
with a Telco, which then forwards the information
on to the RIM NOC. The result is that the NOC now
knows exactly where to push a message to. This is
also the reason why a normal data plan is not
adequate to give a BlackBerry push services. The PPG
is able to send a Session Initiation Request to a
device in a connectionless manner using e.g. SMS,
indicating that it wants to push some content to
a specific application on the push client. Content can
be pushed in this manner as well. I think there are two protocols, PAP between a Push Initiator
and the Push Proxy/Gateway, and Push OTA between the Push
Proxy/Gateway and the device. If you're interested, the Open
Mobile Alliance has a lot of technical documents that are
publicly avaiable.
So, yeah, Blackberry's push is special, and it's necessary for them to plug into the telco infrastructure to do this; however, as an app developer, you just have to register with BlackBerry and use their APIs. Regarding the iPhone,I think Apple Push Notification Service is something like a "mini-NOC", that only does notification and isn't as full-featured as BlackBerry's, and is otherwise "push-like" by keeping open a session/polling.