Otherwise roaming fees will kill you. Data roaming is still outrageous.
It's way cheaper to get two or three SIMs on a months flatrate.....do a little bit of google research.
Here is some advice:
UK - TESCO
Germany - Simyo or Aldi-Talk
CH - Sunrise or Lebara
You usually don't pay more than €2,50 per day flatrate, or €9,90/1GB flat or €19,90 flat/month.