The matter is a bit more complicated.
Some 50? years ago, �shall � was always used for the 1st person singular and plural and �will � for the others.
This had some exceptions, however, whose meanings are still valid today:a) referring to the 1st person, the use of �will � reinforced the meaning of �will � as volition: so the question and answer at wedding ceremonies is �Yes, I will �, meaning I want, I assert what I really want. (remember the noun �will � and its meanings! and if you want to go further, read Shakespeare �s sonnet!).
b) the use of �shall � for the other persons (2nd and 3rd) also had a nuance in meaning: Thou shallt not kill - in the commandments - means that you MUST not do it because somebody else (God, in this case) says so. And �No one shall enter the premises unless authorised to do so � means there are some regulations which depend on someone else.
So, the use of �shall � and �will � really depends on a kind of interplay of volitions - nowadays �shall � as an auxiliary for the future sounds old fashioned and seems to be restricted to the interrogative form, Shall I....? for offers and Shall we...? for suggestions. We tend to use �will � for all other uses, except, of course, all the little things that the use of the language has crystallized and that make it so fun to look at.
Jespersen and Thomson&Martinet can help you out better than I can do. Good grammar books are a great help sometimes.
Good luck!
