Shall and will are not interchangeable, at least for me. I do use shall, but only in certain situations: 1) When offering to do something. 2) When saying that someone should do something (you see this more in legal context).

In modern English the traditional difference between shall and will has almost disappeared, and shall is not used very much at all, especially in AmE. Shall is now only used with I and we, and often sounds formal and old-fashioned. People are more likely to say: I'll (= I will) be late and 'You'll (= you will) apologize immediately.' 'No I won't!'. In BrE shall is still used with I and we in questions or when you want to make a suggestion or an offer: What shall I wear to the party? ◆ Shall we order some coffee? ◆ I'll drive, shall I? ---from Oxford Dictionary

'Shall' and 'will' mean the exact same thing. They are always interchangeable, but generally 'will' is much more common and 'shall' is usually only used when asking for permission. There's no reason 'shall' can't be used, except that 'will' is more natural. 'Shall' just sounds more formal.