Cellphone shoppers generally judge wireless carriers based on their networks’ speed, size and—above all—reliability. But reliability extends to customer service. Will your carrier be able to help when something goes wrong? And can you get your questions answered in a timely fashion?

With that in mind, we performed a survey of the country’s four largest service providers—AT&T, Sprint, T-Mobile and Verizon Wireless—to determine which offers the best service and which could use some lessons in customer appreciation.

To get a complete view of each carrier’s customer support options, we visited two of their brick-and-mortar stores, placed two phone calls to their tech-support hotlines and tried to connect with them via their Web services. For our tests, we used purchased phones (instead of review units) to help ensure we received genuine user experiences.

Our test beds included an AT&T Motorola Atrix 4G, a Sprint EVO 4G, a T-Mobile G2x and a Verizon Wireless Motorola Droid X. To ensure our testing was fair, we posed the same three questions to each carrier’s service representatives: “How can I tether my phone to my notebook,” “How can I upload photos from my phone to Facebook?” and “How do I improve my phone’s battery life?”

We visited our first AT&T store at 7 p.m. EST on a weekend and waited 20 minutes before Wayne approached us. Despite the small crowd, our customer service rep took the time to demonstrate how to upload a photo to Facebook, making sure we could repeat the steps on our own. He then correctly explained that in order to tether our phone we would have to sign up for a 4GB tethering plan at $45 a month.

When it came to our battery-life question, the AT&T associate told us to reduce our display brightness, before telling us to look into purchasing a secondary battery or battery charger, skimpy but certainly useful advice.

We walked into our second AT&T store at roughly 8 p.m. on a weekend and were immediately greeted by Kim. After showing us how to upload photos to Facebook, she informed us that tethering our phone would require signing up for AT&T’s tethering plan. On our battery question, Kim correctly suggested we turn off our phone’s radios when not using them and reduce our screen brightness.

AT&T’s website was easy to navigate and find answers. After entering our account information, we were promptly connected with Cameron via live chat. He told us how to set up a tethering plan and provided us with a user manual for uploading our photos to Facebook. He also helpfully mentioned that apps that update in the background will drain battery and told us to update them less often. The AT&T rep went on to rightly point out that using our phone’s 4G connection would put a strain on our battery’s performance, but he failed to tell us that using Wi-Fi would be a better choice.

When we made our first call to AT&T, we were put on hold for roughly 2 minutes before being connected with Jacob. While friendly, he was clearly in a rush. He accurately explained how to tether our phone. When it came to our battery life question, he correctly told us to turn off our Atrix 4G’s Bluetooth, wireless and GPS, and to reduce our display brightness.

To upload our photos to Facebook, Jacob told us to simply follow the app’s instructions, something he said he does all the time. This advice isn’t wrong, but he neglected to mention the option to upload pics directly from our Móviles Dual SIM’s Gallery app.

During our second call, we waited on hold for less than a minute before Jesus in Nevada picked up. While he was personable, Jesus’ thick accent made understanding his advice difficult. It didn’t help matters when he gave us a circuitous explanation for uploading our photos to Facebook, which involved opening the camera app instead of the photo gallery. And while the rep accurately answered our tethering question, he couldn’t provide any tips for improving our device’s battery life besides checking the ’celulares touchs notification bar for running apps.