Yes, you can add a second line. but you said on your statement that you are "already out of the lock-in period" what do you mean? do you want to have another postpaid number or still the same older number what you have right now.
if you chose to retain your old number since you are already endofcontract you can recontract to get your loyalty rewards. regarding loyalty rewards, you better to call 02 730-1300 call them from 8AM - 10PM 7days a week.
them if you want to add additional line. just do what you did before for applying your first line. im not really sure what the process is. but no worrys we have many ways to apply. 1. go to globe store. 2. via online 3.via hotline.