People don't use "shall" in casual speech, especially in America. It means exactly the same as "will," but the person who uses it just wants to sound smarter. A long time ago it had a purpose, and here's the way it was "supposed" to work: There were two ways of expressing the future - a normal way and an emphatic way. Normal way: I shall, we shall, he/she will, they will, you will Emphatic way: I will, we will, he/she shall, they shall, you shall But I don't think anyone really used that in speech. I concur with JacquiD on usage of shall. Her examples number 2 and 3 are the only times I can think of where you can't replace "shall" with "will."

Shall is used in different ways. 1) To say something is expected to happen in the future ' We shall arrive tomorrow evening' ( 'will' is used more often in this sense) 2) Used to ask for someone's opinion. 'Shall I call a taxi?' (You can also use 'should'). 3) Used to make a suggestion 'Shall we go to the cinema on Sunday?' (normally only with 'I' and 'We') 4) Used to give a command or to say that you will or will not allow something to happen. 'You shall leave at once'. 'They shall not pass.' 5) Used in laws or rules to say that something is required. 'The jury alone shall decide the verdict.'

Shall is an auxilliary verb and is used in the following ways: 1. Used before a verb in the infinitive to show: a. Something that will take place or exist in the future: We shall arrive tomorrow. b. Something, such as an order, promise, requirement, or obligation: You shall leave now. He shall answer for his misdeeds. The penalty shall not exceed two years in prison. c. The will to do something or have something take place: I shall go out if I feel like it. d. Something that is inevitable: That day shall come.