Investors will be closely monitoring AT&T ( T)'s fourth-quarter results Wednesday to gauge the health of the telecom market.

Analysts estimatethat the telecom behemoth will report revenue of $31.35 billion and earnings of 65 cents a share at a time when few firms have visibility into their long-term performance.

AT&T, like its rivals Verizon ( VZ), Sprint Nextel ( S) and Qwest Communications ( Q), faces the challenge of shrinking enterprise budgets and super-cautious CFOs.

Bank of America analyst David Barden explained that he will be looking to see how the economy is affecting AT&T's volume-based voice revenue, the migration to IP from legacy data systems, and, crucially, the company's forward-looking statements.

"We expect guidance to be less detailed than in the forecasts provided prior to 2008," he wrote, in a note released Tuesday.

Many companies, not just in the telecom sector, are struggling to project even short-term revenue. AT&T rival Verizon, for example, was unwilling to offer forward-looking revenue guidance in its fourth-quarter results, released Tuesday.

Investors reacted negatively to Verizon's fourth-quarter results, heralding a broader slump in tech stocks that saw AT&T's shares slip 90 cents, or 3.35%, to $25.93.

Set against this backdrop, Barden is also keen to measure the economy's impact on AT&T's wireless and wireline businesses, particularly after the latter proved problematic for Verizon.

"Key issues we are watching into the quarter include wireline performance and how wireless, cable, and the economy are impacting line loss relative to one another," he said, adding that Apple ( AAPL)'s recent performance could also impact its AT&T partner. "Results from Apple imply that fourth-quarter iPhone 3G sales fell short of the third-quarter launch period, in line with our expectations, which should push up margins sequentially."

AT&T fell short of Wall Street's earnings target for its recent third-quarter results, due to a too-strong performance from Apple's iPhone 3G and its own weak wireline results.

At that time, The company's earnings took a hit from the July 11 introduction of Apple's iPhone 3G, a product for which AT&T is the exclusive authorized U.S. service provider. As part of the iPhone subsidy agreement between the two companies, AT&T's profit was cut by about $900 million, or 10 cents a share.

Bank of America analyst David Barden will also be on the lookout for the possible effects of AT&T's recently-announced corporate restructuring, which put the company's Mobility CEO Ralph de la Vega in charge of consumer operations covering wireline and wireless.

A chill wind is certainly blowing through the telecom sector on the eve of AT&T's results. Shares of telecom peer Verizon, for example, closed down more than 3% Tuesday, with Sprint and Qwest falling 2% and 4.4%, respectively.