France officially gained its fourth mobile network operator Tuesday when Iliad (Euronext: ILD), best known for disrupting the country's fixed-line triple-play market, launched its Free Mobile service.

And, true to form, Iliad (better known for its Free brand) kicked off its new service with aggressive pricing designed to undercut France's three existing mobile operators -- Orange France , SFR and Bouygues Telecom .

From today, Iliad offers a monthly mobile plan for €19.99 (US$25) per month without a contract that includes unlimited calls, texts, MMS and Internet usage via Wi-Fi or 3G with a cap of 3GB. The operator claims the price is more than two-and-a-half times cheaper than rival offers.

In addition, Iliad unveiled an entry-level price plan for €2 ($2.50) per month with no contract that includes 60 minutes of calls and 60 SMS messages per month, which the operator says is four times less expensive than rival offers.

For existing Iliad fixed-line customers that already have its Freebox home gateway, the unlimited mobile plan will be offered for €15.99 ($20) per month and the entry-level plan will be available for free.

Iliad crowned its mobile service launch with news that it will offer Apple's iPhone 4S from Jan. 27. The 16GB version of the device will cost €1 ($1.20) for the first month and €19.99 ($25) per month for a 36-month period, while the 8GB device will cost €1 ($1.20) for the first month and €15.99 ($20) per month for three years. The operators will start taking iPhone 4S orders on Jan. 20.

Why this matters
With Iliad's Free on the French mobile scene, life just got more difficult for Orange, SFR and Bouygues.

For Iliad, which has always been France's upstart service disruptor, today's launch means it can finally add its own mobile services to its broadband and IPTV offerings.

And there is likely more service innovation to come from Iliad. For example, it is understood that the operator is planning to integrate femtocells into its Freebox home gateway and offer the indoor mini mobile base stations for free.

For more
Here's Iliad's mobile odyssey:

— Michelle Donegan, European Editor, Light Reading Mobile