I have done something like this:
<telerik:RadTabStrip ID="RadTabStrip1" MultiPageID="RadMultiPage1" runat="server"
AutoPostBack="true" SelectedIndex="0">
<Tabs>
<telerik:RadTab Text="Tab1" Value="1" >
</telerik:RadTab>
<telerik:RadTab Text="Tab2" Value="2" >
</telerik:RadTab>
<telerik:RadTab Text="Tab3" Value="3" >
</telerik:RadTab>
</Tabs>
</telerik:RadTabStrip>
<telerik:RadMultiPage ID="RadMultiPage1" runat="server" SelectedIndex="0" RenderSelectedPageOnly="true" >
<telerik:RadPageView ID="Tab1" runat="server" >
<telerik:RadGrid ID="RadGrid1" RenderMode="Lightweight" ClientDataSourceID="RadClientDataSource_RadGrid1" ... >
<MasterTableView >...</MasterTableView>
</telerik:RadGrid>
<telerik:RadClientDataSource ID="RadClientDataSource_RadGrid1" runat="server">
<ClientEvents OnCustomParameter="ParameterMap" OnDataParse="Parse" OnRequestStart="onRequestStart" OnRequestEnd="onRequestEnd" />
<DataSource>
<WebServiceDataSourceSettings BaseUrl="../../../myWebService.svc/">
<Select Url="GetStream1" DataType="JSON" RequestType="Post" ContentType="application/json; charset=utf-8" EnableCaching="false" />
</WebServiceDataSourceSettings>
</DataSource>
<Schema ResponseType="JSON">
<Model>...</Model>
</Schema>
</telerik:RadClientDataSource>
</telerik:RadPageView>
...
<telerik:RadPageView ID="Tab3" runat="server" >
<telerik:RadGrid ID="RadGrid3" RenderMode="Lightweight" ClientDataSourceID="RadClientDataSource_RadGrid3" ... >
<MasterTableView >...</MasterTableView>
</telerik:RadGrid>
<telerik:RadClientDataSource ID="RadClientDataSource_RadGrid3" runat="server">
<ClientEvents OnCustomParameter="ParameterMap" OnDataParse="Parse" OnRequestStart="onRequestStart" OnRequestEnd="onRequestEnd" />
<DataSource>
<WebServiceDataSourceSettings BaseUrl="../../../myWebService.svc/">
<Select Url="GetStream3" DataType="JSON" RequestType="Post" ContentType="application/json; charset=utf-8" EnableCaching="false" />
</WebServiceDataSourceSettings>
</DataSource>
<Schema ResponseType="JSON">
<Model>...</Model>
</Schema>
</telerik:RadClientDataSource>
</telerik:RadPageView>
</telerik:RadMultiPage>
Now I succeeded in my attempt: now loads only the first tab (thanks to RenderSelectedPageOnly = 'true' in RadMultiPage1).
In addition, with AutoPostBack = 'true' in RadTabStrip1, and RadAjaxManager, can load other tab on demand.
But I think I have found a bug.
After viewing the first tab, I click on a second tab: everything goes well, the binding of my RadGrid is successful, all calls to JavaScript functions occurring successfully, the call to my web service is done ... everything ok. But at the end of the procedure it raises an exception that blocks the functioning of the entire page (see the attachment).