Hi @hleenders,
Thanks for your post.
Once you've received and activated your order, you'll need to get in touch with our Customer Service Team so they can assist with transferring your existing number to your new iD Mobile service.
You can contact them via Live Chat here: https://www.idmobile.co.uk/live-chat
Regarding the billing period, this can sometimes begin from the point the agreement becomes active rather than the date you physically receive the handset. Customer Services will be able to review this with you and explain the billing dates shown on your account.
We hope this helps, and congratulations on your new phone.
Regards,
Gemma M
The iD Mobile Social Media Team