When the GetDataAndCount method is used the RadGrid client-side data binding you get both data and total items count in a single request. I am sending you a simple example which demonstrates this. Also on the following link
I attached a small video which shows that there is only one request. More information about Client-side binding you could find on the following documentation article:
Additionally on the following links you could find information about: WCF and cookieless sessions
I hope this helps.
All the best,
the Telerik team