Can I use Facebook messenger on iPhone to send a text message to a mobile number with only Wi-Fi?

I'm goung overseas to Vietnam soon and whilst I'm over there I won't have any phone signal (for texting and calling) only Wi-Fi when I'm in my hotel. Is it possible to use Facebook messenger on my iPhone to text my boyfriends mobile number using only Wi-Fi? I know you can send an sms from Facebook messenger on Android but I wasn't sure if you could do that on iPhone. Also if I do, will it say it was sent from my mobile number or through my Facebook? So will it cost him credit like usual or does he need Wi-Fi too?

So I would be using Wi-Fi, whilst my boyfriend would be using his phone credit (as he has no data and won't always have Wi-Fi when out of the house) is this possible through Facebook messenger?

No you can't Facebook Messenger can only be Used to Send a message to Facebook Users you can't use Facebook Messenger to send Text messages to people Using Mobile # Facebook Messenger does not let you do that