I have never left an incriminating text or voice message on anyones phone as these pose as evidence the police and/or government can use to track me down and take me down town. I have had a dealer who delivered to me though it always took him a long ass time and he stopped dealing to me after I got arrested which was insanely frustrating. If you feel safe about texts with your dealer then feel free, I am exactly unsure on how much the police are able to legally gather from texts but the cops down here are dirty as fuck.