Unless you live in a cave with poor Internet service, you know that Apple gave case makers a very big gift in the iPhone 4. The iPhone 4’s antenna wraps around the outside of the phone, so if you touch it in the wrong spot, the signal weakens significantly. Admitting the problem, Apple is providing iPhone 4 buyers a free “bumper” to wrap the phone. Problem solved!

But who wants a bumper when there are cool cases to be had? There’s an interesting pricing trend, too. Of the cases available right now—the market for Apple accessories is valued at about $3.7 billion worldwide, so you know the explosion of options is just getting started—most are priced at less than $30. The iPhone 4 bumper, now free, cost $30 before Apple admitted its antenna woes. Apple is giving away bumpers and third-party cases to iPhone 4 owners. Go to Apple.com/iphone/case-program for details.

But if you need a case today, there are options. Belkin offers nearly 10 iPhone 4 cases as of this writing (all under $30) while Griffin has five (most less than $30). Those two companies could be considered the king of cases, as they have built sizable businesses catering to Apple gadget owners. Other choices include the iPhone 4 Vent Gel Case, for $17, from Florida’s AGF, and the iPhone 4 Ballistic HC Series Case, a rugged model that’s designed for the active iPhone owner. It’s pricey at $50, but if you tend to drop your gadgets and don’t mind a case that looks more at home in a military zone than your pocket, it’s worth the money.

You can bet this will be a huge market come the holiday season. Because now you need an iPhone case just to make calls.