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 Mobile TeleSystems OJSC (NYSE:MBT) and VimpelCom Ltd. (NASDAQ:VIP) both plunged about 10% today after Russian soldiers advanced into Ukraine's Crimean peninsula over the weekend.

So what: MTS is Russia's largest mobile operator while VimpelCom (Russia's third-largest) generates about 40% of its business from the country, prompting investors to brace themselves for any potential hit to demand. Of course, the sell-off is naturally being exacerbated by funds looking to pull money out of Russia entirely, so shareholders shouldn't be too worried over today's double-digit beat-down.

Now what: I wouldn't pounce on today's plunge just yet. While bulls should certainly take Mr. Market's reaction today with a big grain of salt, the strong competitive and consumer demand headwinds that have been pressuring Russian telecoms over the past several months are certainly worth paying attention to. So unless you're willing to accept an inordinate amount of volatility, remaining on the sidelines seems prudent.  

Brian Pacampara has no position in any stocks mentioned, and neither does The Motley Fool. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.