After the 10th call, the person will call you and tell you to meet in Nimbasa to return their Item. When you do, they will be added to your Xtransceiver. Call them to total 30 times, but you can only call from places which fulfill the conditions. 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. Call them a 51st time. wait a day and then call them again and they'll meet you in Nimbasa City and offer to trade, willing to have any Pokémon.
You must call them a total of 51 times then wait a day to start trading. After that whenever you call everyday to trade.