Always available by phone, your chances of being able to talk with me 9:00 - 6:00 (EST), Mon - Fri are pretty good. Or send an e-mail...I check e-mail at least once an hour. Skype me, too...@ medarts. Have the latest version of Skype? You can now view your work in progress, live, right from my desktop. Call for details!
For jobs from $25 - $500, I usually ask for the first half upon delivery of initial ideas I give you, and invoice for the rest when you're happy with the final results; over $500, I invoice 1/3 upon delivery of initial ideas, and invoice the remaining 2/3 over two other payments.
But, each job is different, so I am flexible. Any payment methods sanctioned by Guru.com are fine.