not very smart design. If people are going to wear your shirt, why just have a name and a picture? The best advertising you can do is free, word of mouth, or have people wear your shirts around town. I mean they go EVERYWHERE. you might be an old hermit who only washes and waxes cars and goes to the supermarket. But other people go to church, stores you might not want to go into, stores that you have no need to go into, county fairs, OUT OF STATE events (good for you smaller state people). and also, people HATE to be asked questions, and be bothered. if the number is easy to see / remember, they will call it.
Honestly, would you stop a guy on the street just to get a number off of his t-shirt, yet alone for an automobile detailer? Probably not, you would think "yah I could use a good detail on my car/truck" then go home and bust out the yellow pages and then someone else has YOUR business.
in short, I HIGHLY recomend making it more visible and easy to read.
Not only that, but "Sofachrome" font vertical is harsh on the eayes, and if people normally cant read it at first glance, they give up and move on.