There is no point mining with a N900 even if you could time travel back to the early days and mine the easy hashes, now you wouldn't even mine one block as faster miners would claimjump your blocks every time until the heat death of the universe, your wasted batteries and CPU cycles would just add to the wasted enthropy.
Use this console app as designed for a portable bitcoin wallet, write a QT app if you want a nice GUI frontend.
If you want to get fancy get a square brand credit card reader and utilize the magread app code to add ability to convert national currency to bitcoin so you can accept a credit card for a mobile point of sale.