Call MCI/Worldcom and explain your projected calling patern. They'll set you up with a very inexpensive plan, send you some calling cards & give you 5,000 FF miles on most airlines. If after 5 months you try to leave, they will again give you 5,000 FF mile to retain you as a client.

Pay the bill once a month with a Delta/AmEx card and get double miles from AmEx plus 5 miles per dollar from MCI for every dollar spent.