Contact matching for caller ID

I recently purchased an unlocked iPhone 4 in Canada for use in the Caribbean. I waited a long time to be able to purchase a legally unlocked phone since I am very much against jail-breaking and other methods which are currently in use.

When I activated it and used it with my local carrier I have a problem with incoming calls and text messages not matching contacts in my address book. I was told by Apple's support personnel that the iPhone matches against 10 digits and as such I would need to update my contacts to have the area code prefix. The problem is that the way the carrier sends digits is inconsistent. At times they prefix the number with +1 or sometimes just 1 or sometimes no digit at all before the area code. This causes a serious problem in my tests since it would seem that unless it's an EXACT match (this includes the + character), the contact isn't found.

I am wondering how this is supposed to work and if it is as described, what can be done about it? Can the matching be made looser? The Apple Expert also mentioned a feature called International Assist, however this seems to be a carrier specific feature since I don't see this option in my phone.