Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of communications equipment maker Calix (Nasdaq: CALX) fell as much as 10% in early trading after a Morgan Stanley analyst downgraded the stock to "underweight" from "equal weight."

So what: Calix wasn't the only stock to capture the attention of analyst Ehud Gelblum. He also cut price targets and estimates for Juniper Networks (Nasdaq: JNPR), Adtran (Nasdaq: ADTN), and Finisar (Nasdaq: FNSR), Barron's reports.

Now what: All four stocks could see trouble as a result of lower capital spending by large telecoms. AT&T (NYSE: T), in particular, is apparently cutting back in order to preserve capital needed for the fight to acquire T-Mobile. Do you believe Calix will underperform in the months ahead? Would you buy the company's shares at current prices? Let us know what you think using the comments box below.

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Fool contributor Tim Beyers is a member of the Motley Fool Rule Breakers stock-picking team. He didn't own shares in any of the companies mentioned in this article at the time of publication. Check out Tim's portfolio holdings and Foolish writings, or connect with him on Google+ or Twitter, where he goes by @milehighfool. You can also get his insights delivered directly to your RSS reader.

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