I got asked this question many time, so I thought I write a blog to clarify.
What happens to your Whatapps when you put in another sim card temporary when you are overseas.
Firstly, you will need to know that for Whatsapp, it needs 2 things - a Whatsapp account and internet connection.
Let's talk about internet connection first.
We all know that:
WIFI is one of them;
3G/4G cellular data on your phone is another;
and there is tethering (which is basically using other people's data)
Internet connection allows Whatsapp to know when you are online, to receive the text or media you send to your friend and deliver the same. And of course for them to know if you read the message your friend sent and hence display the BT (blue ticks)
So this part is simple. Whatsapp will work when you are connected to internet. No internet (for example when you're in airplane mode, it doesn't work. Simple as that.
Now the account part which is the slightly more complicating.
Everybody has an account with Whatsapp in which they will uniquely identify by your local number. Say your local number is +65 9888 8888, its unique to you because no one in the world will have this number. Call this number from anywhere in the world, your phone will go ringing, but this is not the point. The point is that they can use a set of number and narrow down to 1 person - you!!
Actually this is really what you need to know for whatsapp to work. No confusing at all.
So what's confusing?
You see, many people come asking me, see, my local phone +65 9888 8888 is the number i use to call, text, Whatsapps, etc. When I go overseas, say I travel from Singapore to Australia. Roaming (more specifically data roaming) is very expensive for Singapore SIM so you won't want to explore that option, especially when you are on a budget trip. So the next best alternative is to buy an Australia SIM card, take out my Singapore SIM and put in the Australia SIM and use it for the duration of my trip.
So when I call back to Singapore, my Aust. number will show. When I text back to Singapore, my Aust. number will show, when I Whatsapp to Singapore...wait a minute....why is it still my Singapore number?
If you haven't done any setting changes in Whatsapp, and when you send a message to your friend, they will not know from Whatsapp that you are in Australia and they will not know that you are using an Australia number know in your phone.
And why is it so?
That's because the only thing your Australia SIM does is to provide **scroll back to the top of this article** an internet connection for Whatsapps to connect itself to its server. Your account remains unchanged if you left the settings untouched. Your Australian SIM doesnt modify your account to have its number on Whatsapp. That will be scary if it happens, isn't it? )
So don't get confused as to what number to use? It's always your local number.
The only time you need to change number on Whatsapp is when you changed your local number (say you switched your service provider) and you wish to use your new number as your permanent number.
Even when you are changing phone and not number, you're merely telling your Whatsapp that this is my new phone, bring all data from my existing account to the new phone. Nothing has changed actually.
