If a person has a check dated on 1-4-2012 for 1000 dollars can we say that he has 1000 in his pocket now?

Technically the money is not in their pocket. The check must be deposited or cashed by the person it is written out to, or otherwise endorsed. If the payee does not cash or deposit the check, they cannot give it out like bills of currency. When the check is deposited, the money is taken out of the check writer's account and deposited to the person it is written out to. If you cash it instead, the institution gives you their money and takes money out of the check writer's account.