Sherman said:
Donegal (even if it sometimes seems like a different country
)
You're dead right, we like to call it
God's Country.
Redbhoy, did you travel through NI to get to Donegal? Did you make our receive any calls while travelling through NI? Or, were you near the border? Some areas of Donegal are covered by UK networks I think.
You can only stick a SIM from another network if you're phone is unlocked, there are ways, but I won't mention them here. AFAIK, if you have a bill phone, it may unlock automatically when your contract period expires, but I couldn't be sure.
I wouldn't go back to having a pay as you go phone (it's six years since I had one), I find that it's too much hassle having to worry about credit etc.
Best bet is to call your existing SP and tell them what your usual usage is, and see if they can recommend a better plan for you. Even better, do the research yourself, both on tariffs offered by your existing SP and others out there. I don't think that Vodafone are as competitive as other SPs wrt to text bundles, although you can but them at a more competitive rate than paying for them individually.