Six years after the Ericsson R380 became the first commercially available handset to use Symbian, the Nokia 3250 has become its (more musically-oriented) 100th descendant.
Symbian said it has shipped 70.5 million phones since the company was formed.
Speaking to ZDNet UK before the announcement, Symbian's chief financial officer, Thomas Chambers, said the milestone comes at a time when the company is beginning to concentrate more on the mass market.
Symbian currently has 10 licensees and 66 devices on the market. Chambers said that 56 more products are currently under development.
He predicted that in addition to further business models, upcoming Symbian-powered phones would include a TV handset, more music devices and handsets sporting 5-megapixel cameras.
Although stressing the company's desire to move further towards consumer devices, he admitted that "some of this functionality isn't required in the cheapest of cheap phones. But you will see people wanting more from their devices. If you're going to use Symbian, you want to do more than make phone calls."
Explaining, Chambers said the operating system "fits the purpose in terms of memory footprint, power consumption, multitasking, multithreading and security."
"It's engineered for mobile phones as a complete solution," he said. "We then work closely with the user interfaces. We have things like (pen-based graphical user interface) UIQ, which works on top of Symbian. We're moving into a position where a licensee can take our UI and OS and know they'll work together."
However, he admitted being concerned about.
"We're always worried about Microsoft. It's huge, and if it wants to get somewhere it will," he said. "Windows CE is a force to be recognized, but before we get carried away, I'd expect to see them sign up some more licensees."
"In terms of coming together and making a device, (Linux) has potential," he added. "The problem is you have to do a lot of work on top of Linux to make a phone."
David Meyer of ZDNet UK reported from London.