have you tried having your phone plugged in when you do it? what i do though is i have the universal messaging inbox. it will listed as messaging in your phone. touch the messaging icon>touch the universal inbox (everything from text messaging to emails will be in here)> touch the home icon on the right hand side of your phone underneath the mangifying glass and u turn arrow and house looking button>touch select all>touch delete. this will delete from your computer/laptop as well.