The article doesn't state how the cut-rate airline will provide cell calls and text messages: It's likely that they are in discussions with OnAir, mentioned late in the article, as that firm is the only one I'm aware of that's prepared to launch in-flight cellular service and, later, broadband over Europe. Ryanair keeps fares low—sometimes as cheap as £1—by charging for every thing, including checked baggage. This allows those who need extra services to subsidize everyone else. Even with a la carte on everything, many passengers pay much less overall.
I thought it would be against the philosophy of Ryanair to install expensive equipment on board planes, such as cellular picocells, but OnAir has been telling me that the retrofitting cost and the weight of their gear are both relatively low. The weight is especially low--about half a passenger's worth. Ryanair's proposed per-minute calls are in range with what OnAir has been suggesting as guidance: £1.80 to £2 (about $3.50 to $4.00) per minute and 40c (70¢) per outgoing text message.
This is a lot of revenue to capture, potentially several hundred pounds per flight, which would easily justify equipment costs. Add broadband on top of that eventually, and there's even more money to be made quite easily. The Irish Examiner makes a rough estimate of £60m for one call per 30m passengers for one minute per flight. More likely, some passengers will talk through entire flight, spending £100 on business calls and other will never use the service.
This article notes that OnAir is now publicly mentioning Air France as an upcoming cell partner--their planned first, in fact. British carrier BMI and Portuguese carrier TAP have both been mentioned before as service partners. [link via TechDirt]