That all makes sense. Particularly given that the business voice and fax lines are VAT-recoverable and tax-deductible, we are talking of far from a fortune, so I think there is a limit to how far it would be worth going in search of 'clever' alternatives!You have to arrange the porting process with the new provider before the BT service is terminated, then the number can be transferred. Be warned though, trying to operate fax over VoIP can be fraught with difficulties. And as you're using wireless internet service, VoIP of any sort could cause a lot of problems, depending upon how it's configured, usage in the area, etc.
Kind Regards, John