Calling Mark: (power on) (phone key) M-A (send) - hitting the phone key automatically brought up the dialer, which did double duty as contact search.
Adding a new event to the calendar: (power on) (calendar key) (enter) - and just start typing; you could navigate the fields with the up and down arrows.
Opening the calculator: (power on) (home key) C-A (enter) - the launcher was filterable with the keyboard.
I had a Treo 600 and and then 650 from around 2003 until 2007 when the iPhone came out. The 600 was among the best devices I've ever had. Rock solid, did exactly what it said it did. The 650 would crash randomly just sitting there. Not quite as bad as a Windows phone of the era, but a substantial regression.
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.
“Minimize Taps
Most information about that data should be accessible in a minimal number of taps of the stylus — one or two.
Desktop user interfaces are typically designed to display commands as if they were used equally. In reality, some commands are used very frequently while most are used only rarely. Similarly, some settings are more likely to be used than others. On Palm Powered handhelds, more frequently used commands and settings should be easier to find and faster to execute.
• Frequently executed software commands should be accessible by one tap.
• Infrequently used or dangerous commands may require more user action.”