Also check this 4 solutions for the same problem:


1- [PROPOSAL] Untrackable addresses: https://bitcointalk.org/index.php?topic=131243.msg1405288#msg1405288

2- Untraceable transactions which can contain a secure message are inevitable: https://bitcointalk.org/index.php?topic=5965.msg87757#msg87757

3- Mine: http://bitslog.wordpress.com/2012/08/06/destination-address-anonymization-in-bitcoin/

4- Gavin's: Bitcoin Payment Messages https://gist.github.com/gavinandresen/4120476

Best regard, Sergio.