Yancy can be called randomly.
Once you have had 10 phone calls, they will call you and arrange to meet in Nimbasa City. They will meet you outside the Ferris Wheel and talk to you there. After that, they will register themselves in your Xtransceiver, however they will only appear in certain areas randomly, the same areas as above, but not limited to a single tile.
As you call them, you will have many conversations about a variety of subjects. On the 30th call they'll tell you they want to meet at Nimbasa City where they'll ride the Ferris Wheel with you. Call them to total 50 times, in the 40th call they'll be 'SOUND ONLY', in the 50th call they'll be wearing their work clothes, and cut the line in a second or so.