Your GPA is weighted and adjusted based on 1. Where you went to school 2. What you majored in 3. Your GPA. All three factors go in together to make a determination. If you were an aviation major, you better have 3.5 or better. If you have a degree in biochemistry (or the like) from a well known school, you could get by with a 2.5 or better. If you have a 2.5 in general studies from a state school, you may want to look into a master's program and be willing to dedicate the time to make good grades. Also, the more recent your time in college, the better your GPA should be. That's how the computer systems are designed to look at applications when scoring an app to be pulled for review.
The guys I've known to get hired at the majors with weak-moderate GPAs have all been asked if their grades were an indication of how well they would perform during training (despite being out of college 15+ years). The ones with a degree outside of aviation were able to use "I realized it wasn't what I wanted to do with my life, so I put more effort into working to pay for flight lessons while finishing the degree" as a valid answer. They were hired. The ones with a low GPA in an aviation related degree couldn't use that answer, and those guys weren't hired.