I've never understood the reason of such a success. I think I may have missed something.
I was ready to understand the advantage of push on the security manager's side when I read some times ago a article about the flows. Indeed, as the flows mostly get out he doesn't have to manage ingress flows. But there are replies and the replies are flow that get in!

I've also understood that it's cheaper the push flow is triggered by the operator when it detects the mobile that requested by the mobile itself.

But, let's think about it in 2005-2006. Today major operators offer illimited data subscription. So it's free to check regularly from the mobile.
Today every smartphone is able to use a standard mail reader (understand a Internet mail reader) to read and send messages, even to include attachments as welle as to check regularly for new mails available.

In conclusion, despite the fact that thousands of users checking their mails every minute or so could overload the operator's bandwidth and thus bring the system unuseful, isn't it more adequate, more standard and more proofed to use a common architecture that have been run for over 20 years that is to say : a standard UA and a standard MTA ?

db