Technicall, I say these cells doesn't work in Nepal. Both NTC and mero mobile do have 1800Mhz but this type of network planning is common in all place. e.g In some places where both NTC and mero mobile only use 850Mhz. So, when you take your cell in such places, probably your cell doesn't work.
      I am only talking technical aspects, I don't have practical experince in this issue.