Is it easy to port my existing landline to VOIP (iTalk) so I can move from ADSL (currently with Flip) to Naked VDSL with Slingshot? (keeping my existing phone number in the move)

Reading the iTalk help pages, they say you can't port your main landline number or a service with broadband provisioned on it!

I am assuming that with iTalk being in the Slingshot family, that they would be able to handle the migration and porting successfully so that when they grab the service from Flip, the push my existing landline number onto iTalk and provision my naked VDSL at the same time (but maybe that is overly optimistic thinking!).

It is for simplicity of the migration and porting that I am primarily considering iTalk rather than another VOIP supplier, but if iTalk won't do it anyway, then I guess I have nothing to lose with enquiring of other VOIP providers about porting my landline number to VOIP, in case someone else can do it.

I have a call with Slingshot sales team lined up for the morning, so they might be able to sort it out for me then, but be better if I know the pro / cons / limitations before they call, so that I can do some thinking and know what to order then.

I guess I am happy to take a day or two downtime on either broadband or phone (or both) if it allowed it to happen, as it would save us a reasonable amount per year going forwards.

I guess in terms of lining up my "plan B" options:
... if the above isn't possible to achieve, can I migrate VDS with landline to naked VDSL down the line?
... are there other VOIP providers likely to help me port my main landline during the changeover?
... any other ideas to make this work?

Thanks for your help,

Mike

ps  I was planning to shift to UFB with Slingshot, but there is a reasonable chance we will move house during this year, and their terms will allow me to move house within an IFB area for free, but if I want to downgrade from Fibre to VDSL or ADSL inside the year, then I have to pay $199 to break contract... which seems crazy (regrdless of whether I stay with Slingshot or not - so why would you stay???). Hence planning to take VDSL now since new house is also in VDSL enabled area. Looking to go "naked" with VOIP to offset the extra cost as we don't use landline a lot, but would want to keep number. Have used VOIP extensively in the past in the UK, so happy with VOIP/SIP technology.