TOPIC: mobile / cell phone in default fields

I have searched and can't seem to find any request for adding a further default field in the required default fields. I have a couple of client websites where they want to collect landline and mobile / cell phone numbers, but at the moment I have to use the custom fields option to collect the mobile / cell phone info. Will this be added to a future verion? Or can you give me some instructions on how to add this field to the default fields.

Thanks.