GeoSIMs Dual Number UK/US SIM will have coverage in 203 countries. Both the UK and US number will roam in all countries and have free incoming calls in the US. The US will become "part of Europe" in terms of calling when in the US.
Much of the additional coverage is in Africa, Middle East, South and Central America and a number of island states. In total an additional 68 countries over our standard GeoSIM.
We are updating our site as we finalise details on call pricing but the
coverage list is here