The actor is famous for his booming voice, will lend his vocal talents to the first 100 customers to buy an 8S or 8X, between Monday the 28th January and Monday 4th February.
To qualify, after making their purchase, customers will need to tweet the official O2 Twitter account, using the hashtag #brianmail.
After the messages have been recorded, they will be uploaded to the voicemail accounts. All messages will be personal to each user, based on their name and interests. The recording will also be forwarded to customers via email, so they can keep the voiceclip on their PC.
“I am thrilled to be lending my vocal talents to the good folk at O2,” said Blessed. “I am planning to have a lot of fun with the voicemail messages, and leave the caller amused, confused and generally bewildered.”
General Manager of Devices at O2 UK, David Johnson, said: “Brian Blessed is a cult hero and a voicemail message by him will make our customers' new Windows Phone 8 by HTC phones even more personalised than before.”
“Recording a good voicemail is always tricky and having a national treasure like Brian record yours for you is a chance that doesn't come by all that often,” he added.