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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This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.