iMessage

my Japanese friends, who have softbank iPhones, told me that I should not send messages to them from my AU iPhone because it's not free.

I have always thought iMessage works from any iPhone to any iPhone even across borders (e.g. send iMessage from my japanese phone to somebody in France) as long as both the sender and receiver phones have data network available at the time of sending (or wifi).

I am not sure why my Japanese friends told me that it's not free, I assume they are just not totally up to date about the concept of iMessage.

Anybody can confirm what's the deal with iMessages across Japan domestic carriers and countries?

Thank you!

I am not sure why my Japanese friends told me that it's not free, I assume they are just not totally up to date about the concept of iMessage.

Your friends are misinformed.

Anybody can confirm what's the deal with iMessages across Japan domestic carriers and countries?

iMessages are free. They may count against your data plan though.

iMessages are free ONLY IF you are on WiFi. They are the same cost as an SMS if you are on 3G/4G. SO they will cost UNLESS you are on WiFi at the time.
Japanese cell phones use email, and I think that is essentially free to use as part of the carrier plan. So iMessages may cost the receiver as well.
Check with your friends as to whom they are concerned about the costs: if it is costing them to receive your iMessages, then you may as well use email: we do with family in Japan, but then we hire a WiFi router so we are on WiFi all the time. We then use iMessage for contacting home. But again, only on Wifi

So looks like we already have two different opinions here. My friends also advised to use the email address instead.
However, technically I can't see why sending iMessage from wifi is any different from sending from data network. If its free on wifi then it should be free on 3 or 4g. Just would add on data traffic.

iMessages are free ONLY IF you are on WiFi. They are the same cost as an SMS if you are on 3G/4G. SO they will cost UNLESS you are on WiFi at the time.

I'm afraid you are mistaken in how imessages works. The whole purpose of imessages is to circumvent sms/mms fees by serving as a parallel messaging system that goes over the data network only. So when you are off wifi you're messages should be sent over your data line and charged as regular data.

However, a lot of people are confused because they think that all messages between iphones are imessages when in fact they aren't. imessages is only supported by certain ios versions and must be turned on by both parties. If one party doesn't have imessages set up then the text will go out as sms (and is technically not an imessage anymore). You can confirm this visually in the messaging app as imessages are in blue bubbles while sms messages appear in green bubbles.

http://www.whistleout.com/CellPhones/Guides/a-guide-to-imessage
http://howto.cnet.com/8301-11310_39-57436368-285/three-imessage-tips-y...
https://discussions.apple.com/message/20106550#20106550
https://discussions.apple.com/thread/5045643?tstart=0
https://discussions.apple.com/message/17477834#17477834
https://discussions.apple.com/message/16802827#16802827