Add ability to use simple text type fields as telephone fields

Problem/Motivation

Once we received a phone call that no phone numbers are sent to the Packeta. This makes a real problem for cash on deliveries as the carrier can't contact the recipient for package delivery.
So, I dig into the module code and found out that there's a hidden telephone setting field there actually. And it only appears if the core telephone field is installed. Also, it would be better if the field was shown as disabled instead of completely hidden, as I would have known that I need to set up another field. A lot of webshops doesn't use that for phone input, they just use the simplest text field.
I'd like to request to support these kind of fields, too for phone input. I looked into the WSDL, and the phone is valid if it is a string that's no longer than 20 characters, so we can use plain text fields.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes