We need to know your carrier. Initially, note that I'm guessing that you are even in Ireland based on your fiancee's location, but this could be an improper assumption. You may be fine using your phone close to normal (with a tad bit of studying). Here is a quick comparison of three Irish providers:

Three

For example, look at Three's rates:

http://apps.three.ie/roaming/pages/d...hree-like-home

Here is data:

http://apps.three.ie/roaming/pages/display/data-roaming

Bottom line, you pay almost the same to use a Three IE SIM in the UK as you do back home. Just make sure your phone remains locked on Three and doesn't wander to someone else.

Meteor

Now let's look at Meteor. It even gets better on voice:

http://www.meteor.ie/do_more/roaming/?linkid=footer

If you're on Meteor, you are better sticking with traditional voice. Note that you need to opt into this plan with the required text.

Vodafone

Now let's look at Vodafone. My quick and dirty study says you are best with Vodafone Passport and sticking to voice:

http://www.vodafone.ie/planscosts/pa...oaming/map/uk/

Both Meteor and Vodafone have ok data roaming packages, but my instinct is just stick with voice.