Trumpet includes three "trumpet" cards without a suit that always trump any other card. However, the rules aren't particularly clear on whether they are truly "wild" in the sense that they could count as a card of any suit. In particular, if you have another card of the suit that has been led, are you allowed to play a trumpet card instead?
In most games with a trump suit, you must follow with a card of the suit that has been led, unless you are void in that suit (have no cards of that suit), at which point you may play a trump card. Given that, I would assume the rules in Trumpet are the same, and you cannot play a Trumpet unless you're void in the suit led.
This thread on BoardGameGeek agrees, so I'd say it's fairly common to play by that rule, even if the original rules are unclear.
I don't know this particular game but from my experiences with various card games trumps are rarely considered matching a suit.
In most games one of the following scenarios is used: