Will

Use will to talk about what we think, guess, calculate, know or predict  will happen at a later time from our "current reality".  Will is commonlyused for stating information, predictions, calculations, or schedules.
I'll call Brad tomorrow with the news tomorrow.  scheduled in futureBrad won't believe what happened .  a guess about Brad's future state of mind
Jason will break up with his girlfriend next week.  a prediction about a futureevent
Jill will be surprised. a prediction about Jill's future state of mind
I wonder how he will say it to her. a guess about a future activityShe will find another boyfriend quickly. a prediction about the future

-We switch to will if the clause is placed within another clause stating opinion:I think..., We hope..., They believe ..., 
and so on.  Mental States.   Be going to is not used after an opinion word.
*I hope that you are goingto  buy a new cell phone.   (*Use will buy.)
I think that you will get a better service agreement. 
I doubt that you will avoid paying extra servicecharges.  avoid (v.) – stop

Speakers unconsciously switch to will if the main verb is go or come. 
I'll come home around six o'clock tonight.   I'll go there around six o'clock tonight.    
En inglés no existen los verbos en futuro, sino que al agregar will, convertimos en futuro al verbo quele sigue: I will come to see you tonight.
I will go - iré 
I will eat - comeré 
I will be - seré / estaré 
I will have - tendré / habré