re: Smartphone - Best Practices
The form factor and functionality of the smartphone is still limited as far as a full-scale, all-in-one solution for most people who practice GTD. Until the full features of the desktop operating system become capable on such devices (probably in about 1-2 more years), they will be quite limited in helping GTD users with the higher-horizon planning, clearing the decks, and processing things into their proper places.
The best practice for a smartphone with these limitations is to find one with functionality that makes for the fastest capturing of your ideas and a way of viewing--by context--the tasks you need to accomplish each day, as well as a way of marking them complete. You will primarily use your smartphone for collection and working off of your lists.
Use a computer-based (or paper-based) solution for brainstorming, higher-horizon planning (e.g., mapping out your projects), processing things into their appropriate places (e.g., Actionables, Reading, Projects, Someday-Maybe, etc.). Your computer-based (or paper-based) solution should also be what you use for your Weekly Review. Think of the Weekly Review as the "War Room" and the smartphone as your on-the-ground implementation of those ideas. You need something with that larger horizon to plan -- computer / paper. But you can use your smartphone to crank through tasks, remind yourself of important things to remember, and--if fast enough--to collect thoughts during the day.
I would also follow mcogilvie's advice to wait until the new job starts before purchasing anything; especially since some of those technological decisions may already be made for you before you arrive.
Hope that helps.