Formal way to call and ask if a place is hiring?

Yeah just call but also keep in mind that these places all have websites that you can check as well. Search the sites see if you can find the jobs tab and fill out the application. After that follow up with a call no more than 3 days after to make sure they received your application and to show your enthusiasm to start as soon as available. If you can walking in is acceptable however with technology available now it is not necessary short of an interview.