Please help me! Should I pay the rent?

I signed a contract with landlord till 8-31-06. In the end of May this year, I phoned the landlord to ask him if we could move out earlier. He agreed then over the phone. Now, we have already moved out from 8/1/06. But the landlord asks me to pay the rent for August otherwise he will sue me.

I have the proof for discussing the earlier moving out in recent email, in which he said that he misunderstood me and he just agreed to put the apartment on market and we could leave if he find some tenants to replace me. Another two related proves are 1). The advertisement of the apartment itself for Aug. 2). The broker who helps the landlord on the issue of renting out.

I need help on law consulting urgently.

Thank you,