Exactly.

I don't want to have to carry this "other device" besides my Phone. My phone should be able to do all of the things those "other [pocketable] devices" do, where those "other devices" are:

• Mobile Phone(*) (with voice, SMS/MMS, and WWAN data)
• Pocketable Linux/Unix computer
• Pocketable Internet (email, IM, etc.) device
• Pocketable full-feature/experience Web device
• Pocketable PIM-type device
• Pocketable Media Player
• Pocketable Game Player
• Pocketable GPS

(* included because, depending on your perspective, the phone might be the "primary device", or the "other device")

Any solution for my pocket where I have to get some or all of those functions by carrying "another device" is an insufficient solution.