Sprint Corp. (NYSE: S) is set to announce its fourth-quarter earnings Wednesday, but (spoiler alert!) we've already uncovered some of the highlights of the past three months. Here's what we know or expect to learn during tomorrow's early-morning call.

iPhone Outlook: Sprint likely activated nearly 2 million iPhones in the fourth quarter, according to estimates from UBS Investment Bank , which notes that this may help device sales, but it could hurt margins.

• Sprint's Q4 iPhone Activations Could Total Nearly 2M

WiMax Woes: The iPhone attention likely came at the expense of Sprint's 4G WiMax device portfolio. Clearwire LLC (Nasdaq: CLWR) only sold 900,000 in the fourth quarter, with most of those sales coming from its majority owner, Sprint.

• Verizon Is Eating Sprint's 4G Lunch

Network Vision: Sprint's Network Vision has gotten a lot clearer in the past quarter, as it's detailed the shutdown schedule for iDEN, mapped out its first, Texas-centric LTE markets and given LightSquared until mid-March to work out its GPS issues.

• Sprint Details iDEN's Death March
• Sprint Gives LightSquared 'Til Mid-March
• Sprint's 4G LTE Texan Triangle

— Sarah Reedy, Senior Reporter, Light Reading Mobile