Yes, the mobile number listed on your site will stay the same. Site visitors will be able to see it and call it. We would change only the main phone number.
The phone number displayed as my office number on the website would no longer be the same?
Correct. Visually on your website, the phone number would no longer be the same. It will be replaced with a call tracking number that would forward calls to your direct line. The call tracking number would have the same area code as your direct line.