Beware of confusion over the voucher validity, and the bundle validity. Under the CPA the actual voucher you get from your dealer (Pick & Pay, CNA or wherever) must be valid to actually be loaded onto your device for three years.
But once it is loaded it no longer has a cash value, which is the criterion under the CPA. There is nothing to stop the cellular provider stipulating whatever expiry limits it wants on the actual airtime or bundles on your phone once they have been loaded.
Interestingly my wife had her first 'CPA experience' with an 'expired' Woolworths gift voucher the other day. Although technically it was too old to fall under the new CPA, Woolworths eventually agreed to honour it anyhow. Gift Vouchers will also have to be valid for three years as they also have a 'cash value'