So this really depends on the number of players in a hand. Ultimately the outcome will be the same but the number of players in the hand determines if a penalty will be applied or not.
Lets just get the easy, no questions about it part done, if there are more than two players in the hand, under the industrial standard poker tournament rules (TDA or WSOP) a player talking like the above example of "For sure I am calling" is speech play which is not allowed unless in heads-up. Some places don't even allow it in heads-up. Now this applies to talking out of turn, the player can say "for sure I am calling" if action is on them. A penalty, or at the very least a warning will be given if it's not their turn to act and they say something like the example given, as it can potentially end up effecting the other players decision.
So on to would it be binding as a call, absolutely it would, if the player was next to act or action hasn't changed.
- So let's say Player A raises, Player B says "For sure I am calling",
this is binding.
- Let's say action is on Player A, they haven't raised but look like they are going to raise, before they act Player B says "For sure I am calling", this is binding. I would also give Player B a warning or a floor call if they've done it before as Player A hasn't finished their turn.
- Let's say Player A raises, Player B is thinking, and before action is on Player C, Player C says "For sure I am calling". In this case this would be binding if Player B calls, or folds. It would not be binding if Player B raises as the action has changed. Player C would also get a warning or a floor call if they've done this before.
Basically if you says "I am calling" in any shape or form, as long as the action doesn't change it's binding. You need to be extremely careful as a player when saying any sentence with the word "call" in it, often players and dealers can mishear and just hear the word call, so you might be saying "Should I call?" and people will just hear call.
An extra little tidbit that you may see, if the player says something like "For sure I am calling I have XX", their hand is dead. No question about it. You can say things that are not true about your hand but you cannot say your hand before showdown.