If I'm/I'll be late this evening, don't wait for me. - I'm is rightWill you write to me if I give/ I'll give you my address? - Either is correct depending on the contextIf there is/will be a fire, the alarm will ring. - Either is correct depending on the contextIf I don't see you tomorrow morning, I phone/ I'll phone you in the evening. - I'll phone is correctI'm/I'll be surprised if Martin and Julia get/will get married. - Either is correct depending on the contextDo you go/ Will you go to the party if They invite/They'll invite you? - Either is correct depending on the context