If our goal is to decipher the message, then it VERY much does matter what type of device was used to transmit that message. If our goal is to determine whether or not there are beings out there sending these messages, then you're right, it doesn't necessarily matter, however in some cases it could. Even if we take these messages at face value, it still doesn't really help us any. They send us a tone, which we represent as a letter, so we might come up with a message that looks like AAABBACCCABA or something. In this culture, the tone that we call "A" could be a letter, it could be a word, it could be an entire story for all we know. It could even just be their favorite song. If this situation were real, there would be no way to tell. However, if they really are sending us tones, we could at the very least take notice of the fact that these beings have ears, probably similar to our hearing range (20 - 20,000 hertz) and that they communicate through tones. That's about the only significant thing we could come up with.