This issue is most likely caused by the logged-in users at the remote site are not using the calling search space for the remote site. A valid CSS needs to be set on either the device, or on the line appearance on the extension mobility profile.
If feasible, set the CSS on the phones at the remote site...and leave CSS blank on the line appearances...this will allow any outbound calls to access local TDM circuits regardless of who is logged into the phone.