Telephone field config

I have 2 questions:

1. what is the best field type to use for telephone numbers in the contact info tab?

2. how can I change a field type for a field that has already been created? I had created a field for telephone numbers as integer type, but I found it was inappropriate because it could no handle numbers beginning with 0. Now I want to change the field type to text or some other suitable one. I can't just delete it so I don't lose the records already stored there. what is the best way to do this?

1. what is the best field type to use for telephone numbers in the contact info tab?

Probably a text field and if necessary add REGEX validation so they can only input in a specific format.

2. how can I change a field type for a field that has already been created? I had created a field for telephone numbers as integer type, but I found it was inappropriate because it could no handle numbers beginning with 0. Now I want to change the field type to text or some other suitable one. I can't just delete it so I don't lose the records already stored there. what is the best way to do this?

Only way to change its type is through database. You'd need to first edit the column in _comprofiler and set its type to varchar(255) then edit the field in _comprolfiler_fields and change it to a text field type.