iMessage & Changing SIM/Phone Number

[MickP]

Hi All,
I'm from Australia (AU) I'll be headed to the US in December, I plan to take my iPhone 6S Plus (iOS10) with me and pickup an AT&T sim whilst I'm over there.
I have a few questions for those a bit more knowledgeable:
-How will iMessage react when I remove my AU SIM Card and insert the US SIM? Do I need to change/update any settings etc?

-Will I still be able to send/receive iMessages from people who have me registered with my AU number with the US SIM in my iPhone?

If it makes any difference I have my AU phone number and my Apple ID E-Mail address registered on the iPhone as 'Send & Receive' adresses.

Any advice would be greatly appreciated.

 

[Applejuiced]

Once you put in the US sim you will not going to receive iMessages send to your Australian phone number.
Tell people to contact you via iMessage using the Apple ID email and not by selecting your number.
You will be able to send and receive using that Apple ID with the att SIM card in the phone.

 

[unclemax]

I just want to add that you can play tricks like inserting your AU SIM into another iPhone, turn it on to activate iMessages, turn it off and voila, your AU number is associated with your Apple ID. Then you can take iPhone 6s, activate iMessages with an America number and you'll have two numbers registered with iMessages.

The reason why you need two phones is because Apple knows which serial number phone activated which cellular number, so once you use the same phone to activate iMessages again your old number will be deregistered.