>> Cell phone
They're available for US$30-40. Just buy one. I think the term you're looking for is GSM and not GPRS.
>> do you think I should not tell the potential employer my short-term stay
Depends on your ethical standards.
>> Will I be able to work with a dependent visa
Nope. You may be able to tutor English or Mandarin on a cash basis though. We'd seen a good site called bigenglish.com (never dealt with them or don't know much about them) which allowed people to hire teachers online.
I'll leave the rest of the questions to people more familiar with ESF than myself