Probably the best time to apply for transfer from non-degree to regular status is in the semester you are taking courses that will bring your total number of credits to 9 or 12 in the MS in Telecommunications program. For example, if you started the first semester taking TCOM 500 and the pair TCOM 501/502 and were successful in both courses, you now have 6 credits in the program. In the next semester, whether you sign up for one 3-credit class or two 3-credit classes (bringing your overall total in the program to 9 or 12 credits, respectively), you should submit your application to enter the program as a regular master's student by the due date in that semester.
HINT: Application for regular status requires three letters of recommendation. If you do not already have these, you should request such letters of recommendation from the instructors who teach you while you are a non-degree student.
Students may have up to 12 credits of courses transferred from non-degree status to degree status. Students should therefore complete their application for regular masters' degree status AND HAVE BEEN ADMITTED to the MS in Telecommunications before they begin any course that will earn them more than a total of 12 credits in their MS in Telecommunications program.
A non-degree student need only submit a copy of their transcript(s) rather than have an official transcript sent to Graduate Admissions under seal. Registering as a non-degree student is also cheaper and the results of the admissions process are known much more quickly. You will need, however, to apply as a degree-seeking student once you have accumulated no more than 12 credit hours as a non-degree student, if you wish to enter into the MS in Telecommunications Program as an admitted master's student.