C.R.
First of all, you and hubby need to be a united front. Your son is being set up for failure - he's being taught to manipulate the two of you. It won't be his fault when he is sneaky when he's older if you guys don't join forces and get on the same page.
With my 3 year old I have found that the simple word "NO" prompts the tantrum. The answer can still be "NO" in my mind, but I don't actually just flat out say, "No, you can't have that." Gotta love the song and dance we moms do, huh!? Anyway, the ice cream thing would have gone something like this at my house (at least, this is what USUALLY works for us) -
"Ice cream? For breakfast!? That's so silly! Tell you what, after you eat a nice breakfast that's good for your belly I will give you a WHOLE SPOONFUL of ice cream - in the morning! You don't even have to use a bowl! We are so hilarious! Hurry, hurry... Eat your cereal so we can have that spoonful!"
Now, you have to be willing to give him the spoonful of it then! Haha. I have ONE child and I pick my battles a lot. I'd say that you have the right to pick lots of yours - more than I need to, for sure!! But really, I can't stress enough the importance of you and your husband being on the same page and working together. My parents were NOT and I played that angle into my teens. But, if it's any consolation, I did turn out to be a successful, honest and kind person (I promise - he'll still be okay, but it's going to make things harder on YOU) and my parents are really wonderful people, by the way! :-)