Plenty of people in Hanoi, Da Nang and Ho Chi Minh City work for American companies they have never visited: project managers at software outsourcing firms, furniture and garment exporters selling to US buyers, and English tutors with students in Texas and California. The work happens in your day. The calls happen in theirs. Here is where the two meet, how a US number fits each kind of work, and what to check before you rely on it.
When do Vietnamese and US working hours overlap?
Vietnam is UTC+7 all year and does not change its clocks (IANA). US Eastern time is UTC-5 in winter and UTC-4 in summer, Central is an hour behind Eastern and Pacific three hours behind, and US summer runs from the second Sunday in March to the first Sunday in November (NIST).
Here is a US working day, 9 a.m. to 5 p.m., in Vietnam time:
| Your client is in | US summer, Vietnam time | US winter, Vietnam time |
|---|---|---|
| Eastern (New York, Boston, Atlanta) | 8 p.m. to 4 a.m. | 9 p.m. to 5 a.m. |
| Central (Chicago, Dallas, Houston) | 9 p.m. to 5 a.m. | 10 p.m. to 6 a.m. |
| Pacific (Los Angeles, San Francisco, Seattle) | 11 p.m. to 7 a.m. | Midnight to 8 a.m. |
None of it falls in your office day, so pick one of two windows. The evening window is for the East Coast: 8 to 10 p.m. in the US summer and 9 to 11 p.m. in the US winter is 9 to 11 a.m. in New York. The early-morning window is for the West Coast, whose day falls mostly after your midnight: 6 to 7 a.m. Vietnam time is 4 to 5 p.m. in California in the US summer, and 7 to 8 a.m. is 4 to 5 p.m. in the US winter.
Mind the date line in your calendar. Your Tuesday 7 a.m. is their Monday afternoon, and a client’s Friday afternoon call lands on your Saturday morning. US clocks go back on November 1, 2026 and forward on March 14, 2027, and each time both windows move by an hour. The US time-zone clock shows each zone right now.
How does a US number work from Vietnam?
The TripoSIM US Virtual Number runs in the TripoSIM app over Wi-Fi or mobile data, so it does not depend on the SIM in your phone. On iPhone, add the TripoSIM web app to your Home Screen. On Android, install the TripoSIM app. To sign up you need an email address, a payment card and a short ID check with a photo ID and a selfie. There is no US address or SSN to provide.
One check comes first. Rules on internet calling differ by country, and on your network a call on the number is an internet call. Check with your regulator or mobile operator, and keep your Vietnamese SIM for calls inside Vietnam.
Texts work differently. A text from a US sender reaches your number in the US and appears in the app over your connection, and verification codes from apps arrive the same way.
Which setup fits your work?
Project managers at outsourcing firms. A US product owner who wants a quick word about a sprint or a bug would often rather call than book a video meeting. Give the PM who owns the account their own number, app and ID check, and put the number and the evening call hours in the kickoff email. A support desk where several engineers answer one line is not a fit: the number is one person’s line for personal and small-business use, and call centers are not allowed. US numbers for remote teams explains when a team needs a business phone system instead.
Exporters with US buyers. Furniture, coffee, seafood and garment exporters get calls about samples, quotes and container dates. A buyer in Los Angeles can call the +1 number on your quote, and you call back in your early-morning West Coast window, before your factory day starts. One person can hold several numbers, each with its own plan, for example one per brand. The importers and exporters page has more.
English tutors. US parents like to talk to a tutor before they book lessons. Your evening is the East Coast’s morning, and your early morning is the West Coast’s after-school hours, which is when many parents call. Let voicemail take calls while you teach. The tutors page covers scheduling across US time zones.
How many minutes does a typical month use?
Take Minh, a made-up example: a project manager in Ho Chi Minh City with a client in Chicago. He has one 45-minute sprint review a week and two 10-minute calls with the client’s QA lead. That is 65 minutes a week, or about 280 minutes a month, inside the 300 minutes a month to the US and Canada. Each outgoing call is rounded up to the next full minute; unanswered calls are free.
In a release month he adds two 30-minute calls and lands at about 340 minutes. One extra pack of 100 minutes, at $5, covers it. Top-up minutes are used after your monthly minutes, stay valid while your number is active and carry over when you renew. They are not refundable. When the client calls him instead, those minutes do not touch his allowance: calls to him come from a separate fair use of 300 minutes a month. The cost calculator works out your own month.
What should your contact page and voicemail say?
Give two windows, both in US time, so a client on either coast knows when to call:
US line: +1 (your number). Based in Da Nang, Vietnam. I take calls Monday to Friday, 9 to 11 a.m. Eastern, or 4 to 5 p.m. Pacific. Leave a voicemail at any time and I will call back within one US working day. For written questions, email (your address).
Write “call or email”, not “call or text”. A US area code makes you easy to call; it does not give you a US office, so name your real city. Most calls will reach you while you sleep, so the greeting matters: messages can be up to 2 minutes, up to 30 a month, kept 30 days. The voicemail guide covers setup.
What can’t the number do?
- No sending texts. It receives texts only. For chat, clients can use email, your team’s chat tool or WhatsApp, which you can set up on the same US number.
- No calls out beyond the US and Canada. Use your Vietnamese line for local numbers.
- No 911. It cannot call 911 or any emergency service, so keep your Vietnamese number for emergencies.
- No internet, no ring. If your connection drops, callers reach voicemail. Keep mobile data on as a backup to Wi-Fi.
The bottom line
From Vietnam, plan East Coast calls in your evening, from 8 p.m. in the US summer or 9 p.m. in the US winter, and West Coast calls in your early morning, when it is still the afternoon before in California. Give US clients and buyers a +1 number with both windows in their time zone, and let voicemail cover the night. Check the rules on internet calling first, then test calls with the ten-check reliability test. The plans page has both plans: $100 a year or $12.99 a month.