This estimate is also not taking into account carrier pass-thru fees, regulatory fees, phone number maintenance fees, etc. The idea that you can send 100K sms segments for a few hundred bucks just isn't true, even in the US. The pricing on these things gets way more complicated than what the marketing pages seem to indicate.

By way of example, my company is sending ~1.5M segments per month at a cost of a couple tens of thousands (I can't say exactly, obviously). This boils down to the fees that I mentioned, international examples that you gave, as well as the differences between SMS and MMS messaging where it's not always clear what counts as MMS (multi-byte encoding, anything with an attachment or URL, >N segments per message where N changes based on delivering carrier, etc.) It gets... Wonky.