Not completely, there are situations when you would use the simple future in which you would not use the phrasal future.. However in some parts of Latin America the phrasal future is used more than in English so much so that there may be places where we would say "will" and they would say "ir a". http://spanish.about.com/od/usingparticularverbs/a/ir_expressions.htm http://spanish.about.com/cs/verbs/a/future_uses.htm
I think it works fine as a translation, but "I will" would be used with the future tense of iniciar (iniciaré). I agree it's frustrating when there never is an exact translation, but they want you to use their version. Anyhoo when I see a present tense of ir, I try to put in the gerund going in the answer. Hope this helps.
I guess that with the 'ir+a+infinitive' structure, there is an earlier indication to a listener of a future tense (rather than waiting for the end of the verb) and maybe it is simpler all round. Brazilians seem to prefer a similar phrasal future in their spoken Portuguese so they too may need to "use it or lose it" - where 'it' is the 'pure' future tense.