I'm going to NYC tomorrow and continue to California (Los Angeles, San Francisco, Sacramento, Yosemite, Joshua Tree) on Wednesday. I need a prepaid SIM card to stay in contact with my friends and relatives in the states and for emergencies.

I just looked it up on the T-Mobile homepage, $6.99 for 30min, looked ok, but won't ship before Monday and arrive on Wednesday. Other option: pay $9.99 in a T-Mobile store.

Other convenient and cheap options?