Since you're locked in, maybe a third party service might help. Something like Google Voice perhaps. Or one of the skype compatible apps with messaging. I think those will also text message as the desktop versions do.
Using the Google Voice app takes more steps, but I imagine is more convenient than sending a message over and over. I haven't actually used it for texting, but the sms option is in there. I think international sms might even be free as I can't find the rates for it, and I just sent an sms to a foreign sim I have and my Google Voice balance didn't change.
Also, there are international texting services that are simply intended to save money on international texts, but in your case would save money and maybe work better. I haven't cared about those in a while but there are lots of websites out there. Many look sketchy though.