Hi. Assuming you RESTART the tablet after inserting the SIM cards. The Netsurfer range by Future Mobile Technology generally supports GSM SIM cards from GSM networks around the world with only a frequency band limitation. Frequency band should however be no issue if you bought your Netsurfer locally/domestically. If you bought it second hand on the other hand, then it's IMEIs may have been blacklisted after being reported lost or stolen. In the extreme, you may sadly have a fail SIM chip :(