I would like to Thank you all for your inputs.

 Getting $15 data plan from your service provider  and using the wifi at home, library, university area where there is  free wifi, is it allowed in the Smart phone by ATT?? Or is it like whenever you use wifi it's gonna reduce from your 200 MB /$15 plan? Any idea???? Is there a way you turn the ATT wifi off and use home wifi on it when you are at home? Please advice.

@Marulez, the software I was talking about is for medical students and MD and  paramedics.And that has an app for blackberry, iphone or android. Thank you.