Rogers Wireless and Fido have extended their free tethering offer through May 3, 2010. In an email sent out by Rogers, the companies explain that the promotion, which was launched this summer, was set to expire on December 31, and provides tethering at no extra charge to customers with a data plan or data add on of 1 GB or more, including the iPhone 3G and iPhone 3GS. In addition, the email states that “customers who are currently eligible to…