Thinking of swapping my current wireless broadband (RBI) ISP to Spark's Unplan Wireless Broadband together with their wireless landline service so I can continue to have a landline phone number but one thing against this is that the Spark flyer states:

[With the Wireless Landline service] ...."Third-party call cards and calls through other providers won't work in the same way, so you'll need to make any toll calls through Spark"

I don't make that many toll calls but when I do I use the Kia Ora card (from compass phone cards) that charge 0.019 cents/minute whereas Spark will charge 24 cents/minure. With the Kia Ora card, I dial a toll free local access number (eg Auckland 965 0103, Wellington 928 0103, Christchurch 978 0103 etc) to use ther service.
If I was on Spark's Unplan Wireless BB/Wireless Landline service, would Spark somehow be able to block me from dialing a local number (eg above) to block me from using the phone card and if so, is this even legal?

Thanks.

PS I have a wireless landline with my current ISP and I can access the local access number with no issues.