Question

Does Apple push use TCP or UDP to deliver messages from their servers to the device?

Answer 1

From the Apple Push Notification Service Programming Guide:

Important: WiFi is used for push
notifications only if there is no
cellular connection or if the device
is an iPod touch. To receive
notifications via Wi-Fi, the device’s
display must be on (that is, it cannot
be sleeping) or it must be plugged in.
The WiFi transmitter must be on
outbound TCP port 5223 and must be
within effective range.

also:

Sandbox and Production Environments

To develop and deploy the provider
side of a client-server application,
you must get SSL certificates from the
iPhone Developer Program portal. Each
certificate is limited to a single
application, identified by its bundle
ID. Each certificate is also limited
to one of two development
environments, each with its own
assigned IP address:

Sandbox: The sandbox environment is
used for initial development and
testing of the provider application.
It provides the same set of services
as the production environment,
although with a smaller number of
server units. The sandbox environment
also acts a virtual device, enabling
simulated end-to-end testing. You
access the sandbox environment at
gateway.sandbox.push.apple.com,
outbound TCP port 2195.

Production: Use the production
environment when building the
production version of the provider
application. Applications using the
production environment must meet
Apple’s reliability requirements. You
access the production environment at
gateway.push.apple.com, outbound TCP
port 2195.

finally:

General Provider Requirements

As a provider you may communicate with
Apple Push Notification Service over a
binary interface. This interface is a
high-speed, high-capacity interface
for providers; it uses a streaming TCP
socket design in conjunction with
binary content. The binary interface
is asynchronous.

The binary interface of the production
environment is available through
gateway.push.apple.com, port 2195; the
binary interface of the sandbox
(development) environment is available
through
gateway.sandbox.push.apple.com, port
2195. You may establish multiple, parallel connections to the same
gateway or to multiple gateway
instances.