Cell Phone Problems
The scenario: Your cell phone won't call, or its internal speaker and microphone are broken, or the display stopped working, or some unholy combination of the three.
Generally speaking, cell phones either work or they don't, and there's not many ways for a user to fix anything unless they're comfortable with opening it up (and thereby voiding the warranty). You can try updating the firmware yourself from the phone manufacturer's website, and if you have access to other similar phones from the same carrier, you can try swapping the SIM Card, battery, or removable storage to see if it's a problem with the phone or one of the components.
Prepare for your call/store visit: You'll probably need to contact your cellular provider, not the handset manufacturer, for support. While manufacturers may provide a warranty, it's usually serviced through the carrier. The iPhone is the notable exception--Apple supports it, not AT&T.
If you have network access issues, call tech support to see if they can help. For phones with manufacturer defects (like a DOA handset or a model with a common software glitch) or other handset issues, you can get better, faster service and have an easier time getting a replacement if you bring your busted handset to your local cellular provider's store instead of opting for over-the-phone tech support. This is because technicians need to see the phone before they authorize a warranty replacement, so the over-the-phone techs will make you send it in and wait for their in-house techs to examine it before you can get a working phone. Do it in-store so the customer service rep can examine the phone and you'll speed up the turnaround by days.
Either way, you'll need your account holder's information--the cellular number and social security number--as well as the brand and model number for your handset. If you've jailbroken or unlocked the device, you'll want to restore it to its factory settings first, because otherwise your carrier probably won't support you.
During the call/visit: Unfortunately, the best approach to making your cell phone tech-support process less painful usually is to be proactive and make a few smart choices before anything goes wrong with the handset. Buy directly from the provider, rather than an authorized reseller, because the provider typically offers a higher level of service (and might not support the handsets that the reseller is selling). Buy handset insurance from your mobile carrier--paying the monthly fee and per-incident deductible is worth it if you're worried about theft, loss, and accidental damage, especially if it's critical to your work or business.
If you do manage to get a warranty replacement authorized, don't forget that the provider usually sends a return envelope so you can mail the broken handset back to them. If you don't do so within a certain window of time, they'll charge you for the full cost of the phone.
Bonus: If you're still in a contract, cell phone providers have the upper hand, thanks to excessive early termination fees and highly subsidized handsets. However, keep track of any accounting errors or billing problems you've had and hold them responsible for crediting it to your account balance. Also, if you're looking to extend your contract or add another line, the customer service reps might be inclined to offer a discount. Finally, some providers (Verizon, for example) have a three-strikes policy for chronic handset problems--if they have to replace your phone under warranty three times, they'll let you pick out a new handset model instead.