"When I got to college, I saw cracked phones everywhere," said the 22-year-old Rockville native, who bought damaged phones on Craigslist to perfect his technique. "Every other person had a cracked screen. I kept fixing them, and more and more people kept breaking them and coming to me."

He now fixes 50 to 70 cracked smartphones a month, catering not only to students but faculty, too. Some of his customers tried to fix the phones themselves first.

Baum charges $70 to replace the screen on an iPhone4 and iPhone4S, and said he keeps his cost low because he works out of his campus apartment and does most of the work himself. He completes most repairs in a half-hour or so. His parts come in large shipments he orders wholesale from China.

"I'd be pulling all-nighters and going to class the next day," said Baum, who expects to graduate in December then focus on his business full time.

Now he's branching out, buying old or broken phones that he repairs and resells through a spinoff business called SellMyOldTech. He runs that from College Park and will start up a service this fall at Salisbury University on the Eastern Shore.

Julian Capps was a University of Maryland senior with a cracked iPhone4 last year when he found his way to onCampus Repairs.

"I dropped it on the sidewalk," Capps said of the cellphone he'd prided himself on protecting. "The screen did that shatter thing. I knew I'd have to go to Apple and pay hundreds to get it fixed."

But he didn't.

"I just sucked it up and lived with it," said Capps, 23, now working for a software startup in Boston. "None of the functions were affected. My plan was to live with it. There was no way I was going to pay a couple hundred dollars."

Then he heard from a friend about Baum's service, booked a repair online and met Baum near campus to drop off the damaged phone. Less than an hour later, Baum returned with the repaired phone.

The phenomenon of college students with beat-up cellphones was the subject of a video spoof by The Onion in December, a "report" that Apple had unveiled the first ever iPhone geared specifically toward college age girls. The thinner, lighter version of the iPhone 5, the spoof video went, comes with a broken screen, "already so shattered you can barely read anything or dial half the numbers."

The satire has some elements of truth. Baum, like Robinson, has inspected several smartphones run over by cars. (Sometimes those can be fixed as long as the mother board is not damaged, he said.)

Then there was the College Park student who picked up her repaired cellphone from Baum, went to put it in her purse and dropped it on the floor. She left the phone, with newly shattered screen, with Baum for a second time.

He recalled her saying as she left, "You're going to tell everyone about this, aren't you?"