Nicaragua doesn't seem to be on the voip radar, and terminating calls to the country certainly looks relatively expensive.
A google search turned up this Miami company that says they will give you a local Nicaragua number and forward calls to that number to any phone number in the U.S. for the minimum cost of $14.95/month for 500 minutes.
http://www.mi505.com/That's not quite the same as a DID in that the Miami company controls the delivery of the call to your number and you still need a U.S. DID or local number.