If you were an old Callblue customer you may be better off taking up GT-SIMs offer to take over the account. Then you can retain the old rates. That is what I did. See the Callblue/GT-SIM site:
http://www.callblue.gt-sim.com/
That said I have all kinds of issues with my Callblue/GT-SIM card recently. I can't receive or make calls and I can't send texts. I can only receive texts. GT tell me they are working on it but I have purchased a TravelSIM as a backup just in case.
However, with O2-UK having better and better deals for roaming (My Europe, My Europe Extra, Chosen Country - Spain and Ireland Bolt-on), plus the fact they give away free SIM cards I'm wondering if I should simply use O2. I'm fairly certain the reliability will be better than any of these roaming SIMS and I can use
www.returncall.co.uk to get even better rates as was pointed out in the Europe forum.