I had the Treo until 2012; the Android headwinds were blowing full speed at that point.

Before the Treo, I had a VisorPhone. Wonderful device, and fit a specific need (no phones allowed in school - great, I can slide the phone out of the back, and continue to use it as a PDA). The thing that killed the VisorPhone for me was PalmOS 3.5's lack of memory protection, combined with a bug in the SMS app. Anybody sending me an MMS message instantly crashed it, requiring me to pull the batteries. Sometimes I hadn't realized it happened for hours, and missed phone calls. MMS messages (group texts, etc) only became more and more common, and when this became a multiple-times-weekly occurrence, I made a move.