Jim Bob is a mentally retarded hillbilly who is often associated with Junkyard Willie. Willie makes him answer customer service calls just to troll with the customers even further because Jim Bob is retarded and doesn't know anything. He has a real hard time staying on-topic with whatever the customer's yapping to him about.
Jim Bob likes to use the vocabulary "lunkhead" to address people he's pranking on the phone, which clearly comes off as hypocritical.
Jim Bob and Willie are really just the same person (the Touch-Tone Terrorists) but with different puppets and convincingly different-sounding voices thanks to voice synthesizers.