I've been even following up with some of the previous interviews to see why I wasn't selected. Mainly my experience and education are the two biggest factors.
Yet why do they look at me if they know I lack them? They all said I interview great. I'm just trying to figure out what it really is.
My guess is that's probably BS. You're right - they wouldn't have you in for an in-person interview, and probably wouldn't even bother with a phone interview, if they didn't think you could do the job.
As someone who's spent time on both sides of that divide, when you're having someone in for an interview you're looking at a couple candidates, and you're pretty sure they're all capable of doing the job. What you're really looking for, then, is the candidate who's going to fit in with the team the best. You'll spend a LOT of time with your coworkers, and things will occasionally get really stressful. You want to make sure that anyone you're hiring is going to work well with their peers, handle stress in similar ways, and that you're not going to spend all your time as their manager dealing with personality conflicts.
So, don't overthink it, go in there, don't get too nervous, and just have a conversation. You've probably got the background to do the job; what you're really trying to do by the second round of interviewing is convince the hiring manager that you're the person they're going to want to spend their days shooting the **** with in the office. That not only can you do the work, but that you'll make the working environment a better place for the company.
Also, if "don't get too nervous" seems like a tall order, I'll let you in on a secret - odds are, the person interviewing you is just as nervous as you are. Trust me, it's surprisingly stressful!
Besides, I'm majoring in Software Development and I want to get into writing mobile apps and that sort of thing.
Careful on this one. If you're interviewing for a customer service job and your interviewer thinks you're looking at it as an avenue into another job totally unrelated to customer service (let's be honest, you won't get promoted to Customer Service Manager and be asked to suddenly start writing apps), you're probably toast. They want a candidate they're not going to have to replace in 16 months time. See if you can spin this into a general interest in the way the telecommunications industry is evolving and how maybe your programming background can help you help customers troubleshoot issues with their phones or whatnot, and ways that this interest of you can help you in THIS job. Absolutely do not make it sound like you're only interested in this job to get to your next.