If I use my UK or US SIM card in Vietnam, will I get free roaming or will there be charges?

Unfortunately, no. If you're traveling to Vietnam with a UK or US SIM card, you will almost certainly incur significant international roaming charges for data, calls, and texts. Free roaming agreements are rare for countries in Southeast Asia. EastESIM offers a much more cost-effective and convenient solution, providing you with a reliable local data connection from carriers like Viettel or Vinaphone. This means you can navigate the bustling streets of Hanoi or explore the serene waters of Ha Long Bay without worrying about a huge phone bill when you return home.