this depends of course on the roaming agreements, on the other side travelsim offers free inbound in countries like russia, turkey, saudi arabia, egypt, tunesia,....
each MVNO has other roaming agreements of course.
also travelsim callback triggering works with USSD and SMS as backup and there are no setup costs per call
another features are the real time recharge and the real time calling history at
www.travelsimshop.com