PCWorld Magazine ran an informative article in November 2010 on the "Top 10 iPhone Annoyances and How to Fix Them." Top problems, among others, on the list include an iPhone that won't turn on or off, or connect to the Internet or connect to Wi-Fi, or has a battery that won't recharge. You can read the advice in this article here, but remember that tampering too much with your iPhone on even a routine fix-it-up may cancel your warranty if you have a more serious repair problem requiring Apple's involvement.
It is noteworthy that the need for independent iPhone repair service is strong enough that web sites have sprouted to offer professional training programs and self-employment careers to those who want to repair them. Descriptions of programs – one online ad describes the work as "Starting a Business in Your Backpack" - indicate that trained repair persons can put together their own tool kit with enough replacement parts to fix several phones before needing to replenish their repair supplies. Once trained and supplied, they advertise themselves available through online service listing sites to make service road calls to travelers in need of repairs.