Interesting observation with iPhone is this normal?

Hi all
I have an interesting observation with my iPhone 4s and asking is the below normal.
I added a contact who has a U.S. cellular number. When I attempted to send them a message it wanted to send a text not an iMessage. So backed out, double check the contact and turns out the iPhone inserted plus 44 in front of the number. Yes I am in the UK. I then recalled that plus 1 is for the U.S. So I put this in front of the number and now all is well. I might know of a feature called dial assist is the culprit here. Am I right here and if so should I turn this off to remove this perhaps helpless assumption that all numbers I add are UK based when truly they're not? Any comments greatly appreciated. Thanks!

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dial assist

I don't know but I'd say that dial assist is the likely suspect. I don't actually know what it does exactly, will it just help you when abroad by finding the international code for you when local phone numbers are given to you? I'd always put the international dialing code in for a contact abroad. O, and when calling abroad from the UK, do it through dialabroad.co.uk, it's really cheap compared to network charges, if like me you know people abroad who don't use internet.