Hi @MG22,
Unfortunately, iD Mobile doesn't support internal number transfers between two separate iD Mobile accounts or plans. This means it's not possible to move your number from your existing SIM-only plan to a newly purchased iD Mobile contract.
The only way to keep your existing iD Mobile number is to upgrade on that specific plan. Alternatively, number transfers are only supported when moving between different network providers using a PAC.
As you've already taken out a new contract, we'd recommend getting in touch with our Customer Service team via Live Chat. They can discuss cancelling the new plan if appropriate and then transfer you to our Sales team, who can help you complete the upgrade correctly while keeping your existing number.
Regards,
Gemma M
The iD Mobile Social Media Team