I'm guessing that most isp's don't give out shell accounts. The ones who do most likely would want a letter of reference from you boss explaining why you need a shell account to do your job.
You could always try social engineering. Chances are if you are asking for a shell account you have bad social skill in the first place so this will be tricky. So just stick to my script and don't **** your pants.
You: Hi I need a shell account
ISP: I just answer phones let me get you some one else.
You: [look at porn while they put you on hold]
ISP2: Why do you need a shell account?
You: because unix is the bomb.
ISP2: How old are you?
You: 18 but iím turning 19 soon.
ISP2: mumbles (Dam script kidz) "click".