Displaying wrong number when forwarding to cellphone

Hi Andrew ,
When im making a call trough my extensions it displays the right caller id. (I am using the app extension routes)Only when forwarding to a ring group with an external number it gos wrong . I`m able to send every id I want, but in this case the call go"s trough te wrong trunk. So the question is :how to force the ringgroup with the external number to use a specific trunk.