Hey there @Sunaina 😊
Welcome to the EE Community, and it's fantastic to hear you're looking to switch over to us!
If you've found a plan that takes your fancy, when you order this online there will be an option at checkout to keep your current number.
You'll just need to request a code from Lebara called a PAC, which allows you to move numbers between networks.
Once you've supplied this, when your new EE SIM first connects to our network, it will bring the transfer forwards to the next working day if requested before 5:30 pm, or the working day after that if it's later than 5:30 pm.
Your account with Lebara would then close automatically once the number moves.
It's also possible to just order an EE SIM without the 'keep your number' option, then supply the PAC at a later date. There's no time limit on when you can do this.
We have more info on how this all works here:
Keeping Your Mobile Phone Number | Mobile Help | EE
Peter
