APNS - what is the cost for sending out a message?

Do the carriers (say AT&T) charge a fee for sending messages throug开发者_运维技巧h APNS? If so, where can I find the pricing details?

As far as I'm aware there are no costs to the sender... The only possible costs would be on the customer's side.. if they do not have an all inclusive data plan or if they have gone over their data limits. But the notifications are absolutely tiny in size data wise.. so that really shouldn't be an issue.

So basically it's sent as data and not through the cellular networks.