picking up Network (ireland)

i have recently changed provider from vodafone to O2. with the new sim in my iphone, I am getting a message 'no service'. I am happy that this is not a problem with the sim as it workes both ioutside the house and also works in another phone in the house

. I have gone through everything at this stage including resetting the iphone, up to date setting etc. Basically it seems as if the iphone (rather than the sim) is impacting on me picking up the network. I have already looked at Apple support and gone through the various suggestions. Any ideas?