How to Keep Your US Number Active Abroad (For Free) While Using an eSIM

The #1 objection smart travelers have to switching to an eSIM is simple: "I don't want to lose my phone number."

You need your US number for Two-Factor Authentication (2FA) bank texts. You need to be reachable by clients who only have your main number. You want your iMessages to stay "Blue." But you certainly don’t want to pay Verizon or AT&T $10 to $12 a day just to keep that line open.

Here is the secret the carriers don't tell you: You don't have to choose.

With a modern iPhone and a Cellesim data plan, you can use a technique called "Digital Dualism." This allows you to keep your US number active for calls and texts for free, using your eSIM’s data as the bridge.

Here is the step-by-step guide to beating the system.

The Concept: "Wi-Fi Calling" Over Cellular

You are likely familiar with "Wi-Fi Calling"—the feature that lets you make calls over your home Wi-Fi when signal is poor.

Modern iPhones (iPhone XS and newer) have a brilliant feature: they can treat a secondary data connection (like a Cellesim eSIM) just like a Wi-Fi network.

When you land in London or Tokyo, your iPhone can use the high-speed data from Cellesim to "tunnel" your US phone calls and texts. Your US carrier thinks you are on Wi-Fi, so they don't charge you roaming fees, but you are actually walking around using cellular data.

The Setup: Step-by-Step Guide

Prerequisites:

• An Unlocked iPhone (XR/XS or newer).

• Wi-Fi Calling ENABLED on your primary US line before you leave the US. (Settings > Phone > Wi-Fi Calling > On).

• A Cellesim eSIM installed (but not yet active).

Step 1: Configure Your Data Lines

When you land abroad and turn on your Cellesim line, your iPhone will ask how you want to use the two lines.

• Default Voice Line: Select your Primary (US) number.

• Cellular Data: Select your Cellesim (Travel) eSIM.

Step 2: The "Cellular Data Switching" Setting

This is the most critical setting to prevent bill shock. Go to Settings > Cellular > Cellular Data.

• Select: Cellesim (as the data source).

• Allow Cellular Data Switching: Turn this OFF.

Why? If you turn this ON, your iPhone might try to be "helpful" and switch back to your US carrier for data if the Cellesim signal dips slightly. That split-second switch will trigger the $10/$12 daily fee from Verizon/AT&T. Keep it OFF to ensure you only use prepaid Cellesim data.

Step 3: The "No Service" Trick (The Ultimate Hack)

To force your US line to use the "Wi-Fi Calling over Cellular" feature, your US line needs to believe it has no cellular connection to a partner tower.

1. Go to Settings > Cellular > Primary (US Line).

2. Ensure Data Roaming is OFF.

3. The Pro Move: Tap Network Selection. Turn "Automatic" OFF.

4. A list of carriers will appear. Manually select a carrier that does not exist or that your US carrier does not partner with (or just pick a random one that isn't the main partner).

5. Your Primary line signal bars should go empty or show "SOS," but your Cellesim line will have full bars (4G/5G).

Once this happens, look at your status bar. It should change from "Verizon" to "Verizon using Cellular Data" (or similar for AT&T/T-Mobile).

Congratulations. Your US line is now "piggybacking" on Cellesim’s data. You can make and receive calls to US numbers for free, and receive 2FA SMS texts, all while walking down the street in Rome.

Keeping iMessage "Blue"

One of the biggest fears is disrupting iMessage. By keeping your Primary Voice Line active (but roaming off), your number stays linked to iMessage.

1. Go to Settings > Messages > Send & Receive.

2. Verify that your phone number has a checkmark next to it.

3. Do not remove your SIM card; simply keeping it electronically active with the settings above is enough.

Why This Beats the "Day Pass"

Let’s look at the math for a 10-day business trip:

• Carrier Roaming: $10/day x 10 days = $100 (+ taxes).

• Cellesim Method: 10GB Regional eSIM = ~$15 - $20.

• Total Savings: $80+

You keep your number. You keep your clients happy. You keep your bank access. But you stop subsidizing your carrier's quarterly profits.

Stay connected on your terms.

Find your Cellesim Plan Here