I appreciate giffgaff is a virtual network, but not having 901 as voicemail is just ridiculous. Every message that appears saying voicemail goes to 901 on Android and on a majority of phones it's impossible to change to another number. Then it resets itself after updates.
Surely there's a way to make this possible, it can't be technically impossible,as it makes GiffGaff look like a bunch of amateurs.
Yes, I did search the labs for 'voicemail' variants and found nothing, if this has been suggested already.