You can unlock a phone set (not a SIM card). Mobile network operators normally have fed unique codes to the handsets they sell to you so that you can not use it with the SIM cardsof any other network. If you can use SIM cards of other networks in your handsets, it means the set is unlocked and can be most probably used in Nepal too. If not, you have to UNLOCK it using some unique codes . For many Nokia and Siemns sets , the codes can be calculated using free softwares on the internet......just google it. But 3G sets are hard to unlock and even if unlocked , u may still have some problem if u try to use it in Nepal as my experience tells me. Good luck and do not hesitate to ask for suggestions if still confused