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: Wireless radio tower operator SBA Communications (Nasdaq: SBAC) is getting a bad signal today as its shares swooned by 10.4% on very heavy trading volume.

So what: You guessed it: SBC is another victim of the proposed merger between Deutsche Telekom subsidiary T-Mobile USA and all-American phone giant AT&T (NYSE: T). Fears that fewer competitors in the mobile space will lead to less infrastructure investment are hurting SBC, American Tower (NYSE: AMT), Crown Castle (NYSE: CCI), and other tower operators to various degrees.

Now what: If consummated, synergies in the T-Mobile deal will undoubtedly damage infrastructure companies and their stocks. But this colossus of a contract stands on feet of clay, much like the proposed but never completed attempt to combine Sprint (NYSE: S) and Worldcom eleven years ago. The final "yea" or "nay" from our regulatory systems will decide whether SBA is trading at a deep discount today or simply suffering as it should.

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