WCF Asynchronous Services and WebHTTPBinding

Hi
I am a newbie to WCF. I have 2 questions regarding WCF services which are
however at the advanced level.
I am using REST style invocation for my services. My service name is GetData
and it would be used by generic AJAX clients and/or ASP.NET AJAX clients.
1. Using the URL, it is possible to invoke the service (REST style). But is
it possible to invoke the Asynchronous version of my method i.e.
BeginGetData(). I believe not, since there is no proxy involved here.

2. Can I use WebHTTPBinding to maintain state the way ASP.Net does and to
enable reliable messaging, security and ordered delivery for my
communication? By default, I know that WebHTTPBinding does not support these.
Is there a way to customize these?

Kindly reply asap as I am already delayed on my design.

Thanks in advance
VIkas Manghani