While  AT&T's (NYSE:T) success isn't as tied to Apple (NASDAQ:AAPL) and the iPhone as it once was, investors watching this week still need to know if increased competition is taking a toll.

There's plenty of it. Sprint Nextel (NYSE:S) and T-Mobile have joined Verizon in carrying the iPhone. All four are pitching deals to get customers to switch, though only T-Mobile has taken the dramatic step of ending subsidies and lock-in contracts. What will that mean for AT&T, whose network operates on a similar GSM band to that operated by T-Mobile?  We'll know more when the carrier reports earnings on April 23.

For perspective, AT&T activated 8.6 million iPhones in the fourth quarter. A good number, to be sure. But for investors, it's the 4.3 million new iPhones AT&T customers activated in last year's Q1.

Wall Street is expecting Q1 revenue to decline 0.20% to $31.75 billion, resulting in $0.64 of profit per share. The company beat earnings estimates in each of the first three quarters of 2012, only to suffer a 4.3% miss in Q4, according to data supplied by Yahoo! Finance. AT&T stock is up about 27% over that period.

Would a beat help AT&T stock rally further? Will AT&T continue to be the top iPhone supplier to U.S. consumers? Tim Beyers of Motley Fool Rule Breakers and Motley Fool Supernova weighs in on these questions in the following video. Please watch and then leave a comment to let us know whether you would buy, sell, or short AT&T stock at current prices.

Fool contributor Tim Beyers is a member of the Motley Fool Rule Breakers stock-picking team and the Motley Fool Supernova Odyssey I mission. He owned shares of Apple at the time of publication. Check out Tim's Web home and portfolio holdings, or connect with him on Google+Tumblr, or Twitter, where he goes by @milehighfool. You can also get his insights delivered directly to your RSS reader.

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