I am afraid it it not as simple as that.Today can be -
I phoned my mother earlier.
I have already phoned my mother twice this morning.
I can't talk now - I'm driving at the moment. (Speaking to a caller on your mobile phone)
I'll call you back later.
I'm going to call her this afternoon.
I'm flying to France early tomorrow morning.
so, we can use all tenses about today.