I'd say BE CAREFUL. Experiment before you commit to anything, especially anything that costs money. VoIP is fantastic ... IF IT WORKS! (I use it from two home locations ... perfect in one, very dodgy and intermittent in the other).
Don't assume it's working just because you get one good phone call either. Look for consistency across a couple of weeks, different times of day. When you are happy with soft phone experimentation, consider hardware options. (I use Siemens S685 IP Dect phones, but there are many choices, and a plain old 40 quid ATA may suit you just fine).
There are literally THOUSANDS of VoIP providers you could use. Don't assume you have to use an Irish one. I hear good reports of Blueface -- good customer service. I found Freespeech.ie cheaper, but then they stopped supporting free incoming VoIP numbers. Still worth a look depending on your needs.
*DO* look at the Betamax family of providers. They are all basically the same shadowy Swiss company called Finarea ... it's just they differ slightly on price. Mostly it's down to a choice of completely free phone calls to most countries' landlines and slightly more expensive to mobiles (but still cheaper than you will get with Irish providers) versus a tiny cost to landlines and even cheaper mobiles. This guy has written a really handy script that generates a Betamax price comparison page that updates every day:
http://backsla.sh/betamax
Again, experiment before committing. I personally use poivy.com ... I have reduced the calls part of my phone bill from approx. EUR 300 per bill to approx. zero, replaced by about a fiver a month to poivy. You won't get blueface or freespeech that cheap, but there may be other reasons to go with them, depending on your needs. You will not be able to get a VoIP in number with poivy or other Betamax family providers. However, with something like the Siemens IP phone you can sign up to multiple providers simultaneously. With dialling plans you can use the cheapest service for different destinations automatically, although managing pay-as-you-go payments to multiple providers may get cumbersome. One of your services can host your VoIP in number.
Hope this helps.