Iphone-to-iphone texts are sent over IP, using some apple database mapping. Regular texts use phone company SMS. There is a widely known bug that if you switch from iphone to non-apple-phone you can fail to receive texts, as apple still tries to use the IP routing. I guess some bug or misconfiguration there could result in texts to the wrong recipient.

As far as I know, there is no analagous VOIP routing for iphone calls: all go through the regular network. So misrouting there would be a much bigger surprise!