When I had T-Mobile, I sent international SMSs all the time. Can’t seem to get it to work properly with AT&T though, but I haven’t really tried too hard. And I have had no problems with either carrier as far as sending a message to a subscriber on another carrier.
I’m not sure how wide-spread this is, but my text-messaging service through Sprint PCS is ridiculously unreliable. I’d venture to say 25% of the messages I send or are sent do not make it. If not for that, I think I’d rely a lot more heavily on text messaging. I send about 40-50 per month as it is.
Do they still make you use the browser to send text messages? Most carriers let you send them directly from the phone’s message center (mobile originated SMS).
From my experience, this wasn’t uncommon in Europe, either. Perhaps it’s more pervasive here, but there are plenty of carriers to which you could send text message in an email formatted phonenumber@mobileserviceprovider.com.