The service, which has finally received regulatory approval after the airline announced plans to launch it in 2006, enables passengers to make and receive calls and text messages, as well as send emails and download attachments.
The in-flight phone calls are not cheap, costing between £1.50 and £3 per minute while text messages cost 40p plus, and emails £1 to £2.
The service was launched by chief executive Michael O'Leary in typical cheap and cheerful style -- he dressed up as a giant mobile phone and bragged that the mobile equipment for each aircraft cost about £100,000.
The technology has so far been installed across 20 of the company's aircraft, but the carrier intends to equip its entire 170-strong fleet over the next 18 months.
It was back in 2006 that Ryanair announced it had signed up with OnAir who are majority owned by aviation communications group Sita and part-owned by Airbus.
In August last year, the airline said it had fitted 10 aircraft with the necessary technology and was planning to launch the service "next week". But the service was not given the go-ahead until this year.
Dubai's airline has provided its passengers with a similar service since March last year and changes £2 per minute for voice calls.
Other airlines have also toyed with the concept, including and , which have trialled the service on single flights.
is planning to introduce a mobile phone service on its business flights service from London City airport and JFK airport in New York in the autumn.