I used to be on the "business plan" that was costing me 70-80 euro per month but I switched to their newer "Clear" plan which means my bills are now 30-35 euro per month. I don't know if that plan would be a good option for you, it gives you unlimited calls to Iirsh landlines and O2 mobiles for 25 euro per month.
When I rang them about moving to the new plan they were offering to give me free voicemail to stay with the business plan and I got the sense I would have got some more things thrown in if I stayed with it.
So, yeah I think there is scope to get some freebies, but check that the plan you are on is the best one for you as a starting point.