I'm studying abroad this semester in Amsterdam, and I recently got a Lebara international bundle sim-only plan. This plan allows me to have unlimited texts and calls, and 5G of data. My question is this: Do I need to turn off imessage to make sure I don't rack up any extra money on my plan by texting US numbers, or does it not matter the location you're texting if it's using data, rather than service? I can't seem to find the answer to this specific question of whether texting US numbers will cause any problems on my EU sim card, or if i should just turn off imessage altogether and use whatsapp instead.
You don’t need to turn off iMessage. It is transmitted over data and has no connection to SMS and your carrier.
The simple answer is no. iMessage messages are not sent via your wireless provider, whether it be Verizon, AT&T, Orange or any other provider. These messages are managed and delivered by Apple, and as such have no impact on your text (SMS) or multimedia (MMS) messaging plans through your provider.
I would recommend turning it off though. You have unlimited texts but only 5 GB of data so you can use your data on something else.