Rulings for Trading via Telephone
What is the ruling for selling or buying thing (trading) via telephone? For example, one wanted to buy a thing from A. A contacted B, someone whom he used to buy things from, and bought things from B using his cellular phone, of course without handing over the things he already bought. Then A asked the buyer to take the things he wanted from B’s place with a higher price compared to the price B had given to A. What is the ruling for such transaction?