If someone could answer my question, I am in search of finding out what premiums do we have here in Illinois for employees that are On-call at work. What do they get paid?

That depends. They may not get paid anything at all.

How restricted is the time they spend on call? Can they go about their business as long as they carry a cell phone or pager, or are they confined to the house? How long do they have to respond to a call - can they respond anytime within the next hour, or must they respond within five minutes?

Being on call, per se, does not require payment. It's when the employee's time is unduly restricted that payment becomes required.

Thank you cbg for reply.
These are non-exempt employees, so for example doing winter season when we get so much snow here in Illinois they have to come before work hours, before Corp office opens to unshavel the snow. And the Manager pays them the on-call.
So that is why we are trying to research is there a specific rate? Premium? On-call employees get?

You need to be careful here. If employees are physically at work, not allowed to leave, but not working, that is not legally "on call", but is legally hours worked. If they are shoveling your driveway, that is certainly hours worked. I am going to include pointers to two different webpages and suggest that you read them.

Now "on call" and the other hours worked rules are just rules that determine if a specific hour is "hours worked". Federal DOL mostly does not care what rate you pay at, as long as it is at least minimum wage, and if you are using multiple rates in the same workweek, that you used the weighted-average method for determining regular-rate-of-pay for overtime calcuations.

http://www.dol.gov/esa/whd/regs/compliance/whdfs22.pdf

http://www.dol.gov/dol/allcfr/ESA/Title_29/Part_785/29CFR785.17.htm