Possible to transfer international DIDs?

[millennium2]

We are US based and have a UK office. Has anyone ever transferred international DIDs to their current US based 3cx server/US VOIP Provider to save money on calling? Or what would be the best way to do this to avoid expensive calls to and from the US and international locations? Are there international SIP Providers? or best to subscribe to two SIP providers (one US, and one UK) and put them on the same 3cx box and designate Outbound Calls per extension?