Hi there @woz72
Below is all the information regarding voicemail activation etc...http://community.giffgaff.com/t5/Using-giffgaff/Your-voicemail/ta-p/3521085#faq_no_1
These are some quick numbers you need to manage your Voicemail.
To ACTIVATE Voicemail - Dial 1616
To DEACTIVATE Voicemail Dial - 1626
To CHECK Voicemail - Dial 443
To set your own Voicemail message dial 443 and follow the prompts.
Voicemail extended ring will set the number of rings before divert type in **61*443*10* and then the amount of seconds you want in increments of 5 secs maximum 30 followed by # then SEND
Voicemail costs 8p/Call, or if you have a goodybag, it deducts ONE goodybag minute, regardless of how long you are on the call.
To hear your voicemail from another phone you need to set your PIN. Call your number. Wait for the voicemail to answer, then press * Then enter your PIN. You will then reach the voicemail menu.