Does anyone have an 027 number that's on Vodafone and use Skype's SMS service?

I like Skype because I can send TXT's to my family overseas for cheap. It means I pay, instead of my work (it's a work mobile) but that I can get replies.

However, since I've been given this phone I can't get Skype to send the verification messages to it, thus I can't change the number Skype sends SMS's from. It's worked before with other NZ mobiles and my number in the UK.

I have a case open with Skype about it and they're working through it, but it's pretty obvious they're just working from a script and have no real idea.

I'm guessing (but I don't know because it's a work phone) that it's previously been a Telecom number ported to Vodafone. Would make sense wouldn't it, being an 027 number.

Does anyone have any suggestions as to what might be the cause, something I could tell Skype? I can't contact Vodafone NZ directly as it's on a company plan.