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sprint doesn't report to credit agencies, so as long as you're paying on time and it doesn't go to collections it won't positively or negatively affect your score.
pay down your current card and wait six months for all those inquiries to fall off your report before applying for any more. use your current card responsibly to build a good reputation of paying on time and in full every month. you likely won't get approved if they see you maxed out and with a bunch of HPs on your report, you'll look like you're having trouble living within your means even if you aren't. six months from now you will be much more likely to get approved as long as you apply when you have 10% utilization on your current card at the most.
You might need to be a little more patient. You are 18, and don't have a credit score yet. But you are doing the right thing by paying them on time. Are you paying them in full? Or just the minimum? Why the rush for a CLI?