Do you enter a Social Contract described by Locke/Hobbes by using government services or must there be a more significent entrance into this Contract?
I guess you mean the Social Contract described by Locke/Hobbes?
As soon as you somehow agreed with the reasons Hobbes/Locke offer for entering the contract you made your commitment. (this includes the pure acceptance of not being threaten by anybody around you)
Why should anybody willingly renounce their autocracy?
-> (translation from German, so please forgive if I missed the original text) John Locke: About the Government
The answer is obvious as he does have all his rights in his natural state but he cannot enjoy them as he has to be afraid of his security and is continuously threaten by the other around him. He also can never be sure of his posessions.
Thomas Hobbes: Leviathan
The people, who naturally love freedom and power entered that self-restrained called government to secure their existens and a peaceful life, in other words to flee from the normal state of chronicle warfare (the natural state of human kind)