Don't waste your time waiting for a call from a Big Four.. Look out for other firms too..
The response below is for your overall applications (big four and others):
It may take upto a week for some respond, or if you do NOT fit into their criteria, they might not call you at all. Some might revert to you via email.
If you have contact numbers of the firms, you can call there, a lot of CA firms are yet to become tech savvy, which you should avoid.. ;) just kidding..
I'd suggest, send it to a few more firms or as many firms as you can. If possible you can personally drop in/ courier or speed-post hard copies of your CV at your preferred firms. Or, at your visit ask their procedure of applying for articleship.
It maybe possible that your branch/ chapter/ council office's notice board may have a list of vacancies at CA firms, you can try there, or have a look into the employment section of classifieds in your local daily, check out job sites like naukri.com/ monsterindia.com or look here:
The funny part can be, you might get a call from a firm you wanted to get in, once you've joined a firm which, initially you weren't much interested in.