Who's to say that we're even on the same frequency as other species (for lack of a better word than "frequency", I feel as though it's the incorrect term in this situation), we've got many different methods of sending signals, digital, analog, the chances of them using the same method as us is so low that it's laughable, we're undoubtedly sending incompatible messages.
Even if man ever does find a way to contact another intelligent species it's almost certain that we'd never be able to speak or understand each others dialects, not because of translation complications, but because of the shape of our "mouths" (for lack of a better term), a Dog for example can be trained to understand commands and may even understand words and their meanings, but no matter how intelligent the dog may be it will never be able to speak a human dialect because it's mouth shape, tongue, etc won't allow it, the same applies to other animals and obviously alien species. HOWEVER there's a chance that if our species became truly integrated and peace was made, through extreme effort our species might eventually be able to understand each others languages, but still speak our own (For example, the way humans and the "prawns" communicate in "District 9", each being able to understand each others language, though not being able to speak it themselves), though such a process would be unbelievably difficult.
These issues will undoubtedly lead to great conflict between our species, whether one side isn't completely fucked up is up for grabs, whether this can be overcome in regards to relations is also up for grabs (like the relationships between nations, but even greater and infinitely more difficult to deal with; for example Germany and England were some of the greatest enemies known to the world, especially in WW2, however now they're close allies, Japan invaded China long, long ago, things are still pretty shitty between the nations). Meaning that trying to communicate with aliens is pointless, we can continue pissing away time and money attempting to call other species, but there'll be no result. The only way to actually come into contact with an alien species is if we physically find them and work from the ground up. GET READY FOR SMOKE SIGNALS *****!
Let's not forget our environment, odds are they couldn't breathe Earth's mix of air and we'd die from theirs, the effects may be detrimental to one species and of a great benefit to the other (unless they've a larger amount of Oxygen than Earth, then their home would be sensational and maybe even prolong our life spans, unless they have different requirements, perhaps they're like Earthen Flora and actually Breathe in Nitrogen instead, the possibilities are unfortunately endless. Though in such a we'd probably attempt to invade their home or vice versa, something I'd support because the idea of a longer life is awesome).
EDIT: In regards to other comments about District 9; one of the greatest, most amazing films to have ever been released, I honestly think it'll stand the test of time and become a classic. Not to mention that of all the "alien encounter" movies out there it's the most realistic, which in a way is kinda of sad, but the universe isn't all sunshine and lollipops.