shared code and ListProvider for Combobox Binding

   Hello,
I try to convert my WCF Ria Services to DevForce. In my Ria Service Application I use a country.shared.cs on Model Site and a CountryListProvider on my Silverlight Client to fill and bind a Country List to a Combobox for example.

In Ria Services all works fine, but in my convert DevForce Application it doens't work. Here I search an equal command for 

public EntitySet<Country> CountryList{

get { return _dc.Categories; }

}

I don't find a EntitySet Command in DevForce for Silverlight. I try to use ObersableCollection, but after I select a new Item in my ComboBox I will lost my Bindings. 

I've try to use DevForce Support, but here I wait last few days of help. :-( What do I need a great tool for  dataaccess, when there are no simple examples for standard bindings, for combobox and so on?

I flat datagrid and dataform with textboxes doens't help newbies as needed.  

Or have someone an example for DevForce Silverlight Databinding to a Combobox with relation Datarecords. 
In my Application I have a Country and City List which have a relationship to a address.

I hope there is someone who can help me and you can understand my english?

Regards 
Dirk