"has been fooling around" is correct and usable in written English.
You can use it to indicate that a person has been occupied with some activities that aren't intended to be serious or productive. Example: He has been fooling around with friends instead of studying for his exams.
The telltale sign that Sony has been fooling around with screen technologies is the fact that the screen is jet black when turned off, rather than light gray as on other Palms.
The US Navy has been fooling around with putting some of those underwater robots on small boats, acting as motherships (motherboats?) that can transit to and from a minefield without setting off the mines, making it a lot easier to get the underwater robots to their mine warfare work sites without having to do the same with your nice new ship.
"Somebody has been fooling around with these numbers," he said to her. "I don't think so, David.
Not the way I needed to," Marty tells the detectives, and there's evidence of that in his violent reaction (in the 2002 timeline) upon discovering his 15-year-old daughter has been fooling around with two college boys.
Sony, and just about everyone else, has been fooling around with OLEDs for quite some time, and they're starting to come up with some pretty clever applications of the technology.
Apparently, Father Carvallia has delusions of grandeur and has been fooling around with sneaky Princess Beatrice.
Joseph Leclerc may have been fooling around on the side, but he was living, according to the 1930 census, at 39 Knight Street with his wife, Dora.
While he was gone, she ransacked the tour bus for evidence that her man had been fooling around on the road.
Growing up, she documented all of her teenage sexcapades in her diary, up until the day her mortified mom discovered the secret text and read intimate details about the boys she had been fooling around with.
Their daughter, Sharia, then 12, noticed that someone had been fooling around with her computer.
And all this time he had been fooling around with arguments, with philosophy and political science.
