Almost all of the teahouses in these trekking regions provide a telephone facility for free. Recently many teahouses have also connected WI-FI subscription and offer it for free, but some might charge specific fees for the WI-FI usage. You can also buy an NTC or Ncell SIM card after you land in the capital city. You can use this SIM card to communicate, and you can use a data pack for internet accessibility as well. As you ascend, the network might be weak in some places. Therefore, SIM-card services might not work everywhere.