Dogs bark. It's what they do. Terriers are purported to be more yappier than some. I don't know any "dog training service" where you send the dog away and they return totally trained. Most training has the owner do the training, and it's more about training the owner how to best deal with their dog rather than train the dog. The major, superior place I'd recommend is Canine University in Malden http://canineuniversity.com/. It's really close (2-3 blocks) to the Oak Grove T station. Their staff is really really excellent with training people to train their dogs. While they have puppy classes, they have mostly adult dog classes. If you call Canine university and explain your issue, they would be able to either tell you the right class to take, or point you at a super-expensive personal trainer who can help.

A few years back when I first got my dog, I went there. He was 5 years old and barely trained at anything. They put him in with "larger puppies" for the first class due to his inexperience with anything, and gave me special training techniques that worked specifically for my dog's learning style. I ended up taking lots of classes with them because not only was it fun, but it's great mental exercise for the dog too. They're big on "clicker training" and I'm sure they can help you learn why your dog is barking and give you tools to lessen the frequency of his vocalization.