I am using Tesco Mobile which uses the O2 network and am on the Clubcard Talk plan.

http://www.tescomobile.ie/priceplans/conductyourplan.aspx

As I have a Tesco Clubcard for €15 a month I get the following (this costs €20 without a Clubcard):

1. Unlimited calls to any network and landlines
2. UNLIMITED any network texts add-on (uses €10 of the €15 top-up)
3. 1Gb 30 day DATA add-on (uses €5 of the €15 top-up)

Note: €5 in Tesco shopping vouchers also buys you a €15 Tesco top-up via their deals site.

http://www.tesco.ie/clubcard/deals/mobile.aspx