SIM Card Activation

Complete guide to activating your Three SIM card, transferring your number, and troubleshooting common activation issues.

12 min read
Easy difficulty
Updated: Jan 15, 2025

Introduction to SIM Activation

Activating your Three SIM card is the first step to enjoying Three's mobile network. This guide will walk you through the entire process, from inserting your SIM to transferring your number and troubleshooting any issues.

Before You Begin

Make sure you have your new Three SIM card, your phone, and your PAC code if you're transferring your number from another network.

Important Note

MyThree Guide is an independent resource and not affiliated with Three UK. For official support, always contact Three directly.

SIM Card Types & Compatibility

Three offers different SIM card sizes to fit various devices. Here's how to identify which one you need:

Standard SIM

25mm × 15mm

Older devices

Micro SIM

15mm × 12mm

Devices from 2010-2015

Nano SIM

12.3mm × 8.8mm

Most modern devices

Three's SIM cards are typically triple-cut, meaning you can pop out the size you need for your device.

Activation Process

Follow these steps to activate your Three SIM card:

  1. Insert your SIM card - Power off your device, insert the Three SIM, and power back on
  2. Connect to network - Your phone should automatically connect to the Three network
  3. Activate your SIM - Visit Three's activation page or call 333 from your Three phone
  4. Follow instructions - Provide any required information and follow the prompts
  5. Restart your device - Once activation is complete, restart your phone
Three Activation: 333 (from your Three phone)

Pro Tip

Keep your old SIM active until the transfer is complete if you're moving your number to Three. This ensures you don't miss any calls or messages during the transition.

Transferring Your Number

If you want to keep your existing mobile number, you'll need to follow the number transfer process:

Using a PAC Code
Online Transfer
  1. Get your PAC code - Text PAC to 65075 from your old phone to get your Porting Authorization Code (valid for 30 days)
  2. Contact Three - Call 333 from your Three phone or use Three's online portal
  3. Provide your PAC - Give the representative your PAC code and details
  4. Wait for transfer - The transfer usually completes within one working day
  1. Visit Three's website
  2. Log in to your account - or create one if you're a new customer
  3. Find the number transfer section - usually under "Manage Account" or "My Services"
  4. Follow the instructions - provide your current number and account details
  5. Confirm the transfer - review and confirm your details

Transfer Timeline

Number transfers typically complete within one working day. You'll receive a text message confirming when the transfer is complete.

Activation Status

After initiating activation, you can check the status of your SIM activation:

Status Meaning Next Steps
Pending Activation request received but not processed Wait up to 24 hours. Keep your old SIM in your phone.
In Progress Activation is being processed No action needed. Process typically takes a few hours.
Completed SIM is activated and ready to use Restart your device and test your connection.
Failed Activation encountered an issue Contact Three support at 333 for assistance.

Troubleshooting Activation Issues

My SIM isn't activating

Try these solutions: 1) Ensure you've correctly followed the activation process, 2) Restart your device, 3) Check that you've inserted the SIM properly, 4) Wait at least 24 hours for activation to complete, 5) Contact Three at 333 if issues persist.

I can't get a network signal

This could be because: 1) Your SIM isn't activated yet, 2) Network settings need updating, 3) You're in an area with poor coverage. Check Three's coverage map, restart your device, or try manual network selection in your settings.

My number transfer is delayed

Number transfers can take up to one working day. If it's taking longer: 1) Check with your previous provider that they've released your number, 2) Contact Three to ensure there are no issues on their end, 3) Verify you provided the correct PAC code.

I've lost service during transfer

It's normal to experience a short service interruption (usually less than 30 minutes) during the number transfer process. If service isn't restored after a few hours, contact Three at 333 for assistance.