Just seen the white rose. Everything makes sense now (I'm from the red rose county).
I don't understand why you won't just pay the 26p and delete the message. I'm assuming that you want to be able to give your number out, and be reached by voicemail if (say) you're driving.
If you have a phone, you're going to get cold called on it. It's not even a case of whether you send a text to I'm a Pop Idol Bake Off (although that sort of stuff doesn't help) - eventually a computer is going to ring you up with its random number generator and leave a voicemail saying you're entitled to PPI.
If you need voicemail, you're going to have to put up with the cost of retrieving it or change to a tariff where voicemail cost is inclusive.