It's a wireless jungle out there. Every day, about 33,000 Americans sign up for a wireless phone service or switch carriers. But how to decide which is best for you: digital or analog cell phones or PCS? A Web site has been designed to help: www.wirelessdimension.com offers tips for comparison shoppers. One important piece of advice: Look at the rate plan before choosing a phone. It's almost always cheaper to go with the package deal that includes a phone. The site also has a formula to estimate your airtime usage.