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 third-largest American mobile communications provider Sprint Nextel (NYSE: S) are singing the blues today, falling as much as 17.4% on truly epic trading volume.

So what: AT&T (NYSE: T) and Deutsche Telekom unit T-Mobile USA just announced plans to merge, thus removing the rumored option of Sprint's merging with T-Mobile. Moreover, this deal would recast the competitive landscape in a whole new mold, where Sprint would become the largest mouse running around the feet of two enormous elephants.

Now what: If Verizon (NYSE: VZ) wants to counter the AT&T offensive by buying Sprint, the company just became about a billion dollars cheaper and more inviting for a Big Red proposal. But that's a big "if," and the AT&T deal that triggered today's action might not pass regulatory scrutiny to begin with. The mobile market just got a lot more complicated, and there are no safe bets here.

Interested in more info on Sprint Nextel? Add it to your watchlist.

Fool contributor Anders Bylund holds no position in any of the companies discussed here. 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 is investors writing for investors.