I am sure this has been discussed before, but I tried to do a search and turned up empty.
A new player will be joining my campaign this Friday. He will be playing a Ranger (level 4) with a Wolf animal companion. His 4th level feat is Boon Companion, which brings the wolf to 4 HD and allows it a stat increase. In order for the companion to know more tricks, understand a language, etc., the stat is going into Intelligence, which would bring it to 3.
Looking ahead, are there any sort of exemptions on the concept of Awakening for animal companions? The spell, as well as the Collar of True Awakening item, stipulate that an animal must have an intelligence less than 3, but it is extremely common for those with animal companions to give them a little bump in this area. Does that essentially exclude them forever from the potential of Awakening?
I think this is a case where the specifics of Awaken would trump the generalities of something else, but I want to make sure I haven't missed anything.
Check out "Monkey See, Monkey Do? An FAQ on Intelligent Animals". It lays out the basics on a lot of your questions.
Also note that the awaken spell itself carries this stipulation:
An awakened animal can’t serve as an animal companion, familiar, or special mount.
At that point, the character is better off taking Leadership and selecting the awakened animal as a cohort if they wish to continue in a mechanically bound capacity, though it isn't strictly necessary as the awakened creature serves the one who awakened it in specific endeavors. (In the case of the collar of the true companion, that stipulation might not apply depending on how the GM interprets the item's description. You may have to convince the newly sentient being that adventuring with you is in its best interest.)