That explains why you don't have competitive incoming call rates. Using a dutch provider and number you are also bound to the maximum EU roaming rates and as I said before the rates you have are undercut by many EU other providers.
Mobile roaming: ?0.40 per minute cap from summer 2010
Also you might want to look at your EU incoming call rates. The maximum excluding VAT is set for 16 eurocents per minute (see above document). Your incoming call rate for Germany is 27 eurocents which is against regulations. Spain 28 cents, not good. Other EU countries are ok, so you might want to take a very good look at that.
SMS is set to 11 cents excluding vat. You charge 15 cents which also seems to be against the maximum set eu rates. The maximum rates are law for all EU providers. You might want to argue that you are not an eu company but you are using an EU platform and are therefore by law bound to maximum rates.
But this is just an advice and I would look into it if I were you.