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 Acme Packet (Nasdaq: APKT) plummeted 20% on Wednesday after the communications equipment maker slashed its current-quarter forecast.

So what: Acme's fourth-quarter outlook was so weak -- management expects EPS of $0.26-$0.28 versus the consensus of $0.37 -- that analysts are being forced to lower their growth estimates yet again. Naturally, CEO Andy Ory tried to calm investors' nerves, noting that while results were hurt by "uncertainty in the North American service provider market," Acme continues to perform "very well" globally.

Now what: For the full year, Acme now sees revenue of $308-$310 million, which is off from its earlier forecast of $315-$320 million. Of course, with the stock now down a whopping 70% from its April highs, you've got to think that a good chunk of that pessimism is already baked into the price. Trying to catch a "falling knife" isn't easy, but given its still very strong position in the carrier market, Acme might be worth a shot.

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Fool contributor Brian Pacampara owns no position in any of the companies mentioned. Motley Fool newsletter services have recommended buying shares of Acme Packet. Try any of our Foolish newsletter services free for 30 days.

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