This may not work for your circumstances. The way I'm working around this currently is to have a primary contact for the ticket, reassign all tickets to the primary contact, and then merge the tickets together. It still keeps the ticket history and works for my needs.

Will this allow one customer to have multiple phone numbers listed in the contact?

This is especially an issue when trying to sell a piece of equipment, and you have the husband and wife calling you separately from their cellphones. Or if you have an employee calling for their company. It would be nice to merge them into one account on EC.