Sonus Networks (SONS) shares are down sharply this morning after the telecommunications equipment provider provided a disappointing outlook for the second half of the year.

Sonus yesterday posted second quarter revenue of $87.9 million and and EPS of $100,000, or less than a cent a share; the Street had been looking for $85.8 million and break even.

However, as is often the case, the issue was with guidance. In a post-earnings conference call with the Street, Sonus said it is “not in a position to reaffirm our previous outlook for the second half or provide revised estimates.”

On the call, CEO Richard Nottenburg noted that the company had set a goal of 20% revenue growth for 2008, “with much of that growth anticipated to take place in the second half.” But Nottenburg said the company now believes that revenue in the second half will not exceed the 10.5% growth it recorded in the first half. Nottenburg said the company is “sensitive to the postponement of CapEx by our customers,” and that it is seeing “downward pressure from our prior outlook for the third quarter and the full year.”

In response, Roth Capital’s Edward Jackson today cut his rating on the stock to Hold from Buy, and cut his price target to $3.50 from $5. Jackson said he is “very disappointed” with the guidance. He cut his 2008 GAAP EPS estimate to 3 cents from 5 cents; for ‘09 he goes to 5 cents from 11 cents.

Jefferies & Co.’s George Notter
repeated his Hold rating on the stock, but also chopped estimates; for 2008 he goes to 5 cents from 9 cents; for 2009, he’s down to 10 cents from 13 cents. “Management’s explanation for very weak guidance has left us scratching our heads,” he writes. “Looking forward, we believe there is still some potential for the company to miss revised expectations…we would need evidence that Sonus can deliver and exceed even these lowered expectations before we can get more aggressive on the name.”

Sonus this morning is down 91 cents, or 21.7%, to $3.28.