The last week of October should be defined by two major earnings releases: Social media giants Twitter (NYSE:TWTR) and Facebook (NASDAQ:FB) are set to post their quarterly results. T-Mobile (NASDAQ:TMUS) will also offer up its earnings, and CEO John Legere will speak at Recode's Code/Mobile event shortly thereafter (along with several other executives in the mobile industry).

On the gadget front, the last major flagship smartphone of 2014 could be unveiled.

Twitter: All about the user growth?
Twitter will report earnings later today, and if recent history is any indication, investors should expect some volatility.

All told, Twitter shares are down around 22% in 2014, but the decline has not been orderly -- far from it. A string of bad earnings reports sent shares tumbling to an all-time low in May, but shares have steadily drifted upward since then, boosted in part by a better than expected quarter in July.

For the third quarter, analysts are looking for Twitter to post earnings per share of $0.01 on revenue of about $352 million -- greater than management's guidance. More important, however, could be its monthly active users, a figure that has seemed to dominate the Twitter story since its public offering.

Last quarter, Twitter reported monthly active users of 271 million, greater than what analysts were expecting. This quarter, expectations are around 278 million to 284 million. Given that Twitter remains largely unprofitable, a bright future still rests on its ability to build a large base of active users.

Can Facebook live up to expectations?
In contrast to Twitter, Facebook has had a phenomenal year -- shares hit a new, all-time high last week ahead of its quarterly results.

Analysts expect Facebook to post earnings per share of $0.40 on revenue of around $3.1 billion. Facebook has already demonstrated an ability to monetize its mobile users, but the mobile side of the business will continue to be key as more usage shifts from desktop browsers to mobile apps.

Early in the quarter, Facebook forced users that wanted to use Messenger to download a separate mobile app. Backlash was widespread, but the app proved popular. Investors might look for Facebook to offer up some color on Messenger's performance, and how a stand-alone app could be monetized going forward.

T-Mobile and a new Droid
T-Mobile will also report earnings on Monday, and though it won't host an earnings calling until Tuesday, Legere may offer up some commentary at the Code/Mobile conference.

In contrast to the larger, more established carriers, T-Mobile has not been particularly profitable -- but it has been growing. T-Mobile has been the nation's fastest-growing carrier for much of the last year, adding millions of new customers with its aggressive "uncarrier" initiatives.

The investment case for T-Mobile has largely centered on its acquisition -- parent company Deutsche Telekom has been actively shopping the network, and several buyers have made their interest public. To maintain that interest, T-Mobile may need to show that it can continue growing its base of subscribers at a rapid rate.

With the addition of the iPhone to its lineup, T-Mobile has been able to offer its subscribers nearly every flagship handset for more than a year. Yet it won't be able to offer the Droid Turbo -- that phone, which may be announced on Tuesday, should be exclusive to its larger competitor Verizon.

Made by Motorola, the Droid Turbo is expected to be a high-end Android device capable of competing with the iPhone 6 and the Galaxy S5. Given its carrier exclusivity, it may not sell in record numbers, but the phone could prove to be the last major release of 2014.

Sam Mattera has no position in any stocks mentioned. The Motley Fool recommends Apple, Facebook, and Twitter. The Motley Fool owns shares of Apple, Facebook, and Twitter. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.