The royal baby will be christened by the Archbishop of Canterbury, the Most Reverend Justin Welby, in the Royal Chapel at St James's Palace three months after he was born on 22 July.
The king-sized christening card will be delivered to St James's Palace today by Premier Christian Radio chief executive Peter Kerridge.
The card can be signed at www.premier.org.uk/princegeorge and features a special blessing written by Premier Christian Radio's Media Chaplain, Reverend Tony Miles.
The blessing reads:
God of Life, we rejoice in the gift of a son to the Duke and Duchess of Cambridge.
We prays for William and Catherine as they love and care for George Alexander Louis. Help and equip them as parents, especially as they make solemn promises before You to nurture their son in the Christian faith.
King of Kings, strengthen this family by your Holy Spirit, that they may use the privileges, opportunities, and challenges that come with their national roles, for the good of all and as a witness to Your Light.
We pray through Jesus Christ our Lord, and for the sake of Your kingdom of love and peace. Amen.
Mr Kerridge said: "As William and Kate make promises to bring Prince George up in the love of Jesus Christ, we know that Christians all over Britain will want to send their blessings to the royal family on this special occasion so we've made it possible for them to sign up to our unique Christening card.
"Current interest levels suggest that upwards of five thousand Christians will probably take part."
The Archbishop of Canterbury talks about the baptism of Prince George in a short film produced by Lambeth Palace and extends an invitation to all parents to consider christening their children.
When Prince George is baptised he will join two billion people around the world in "the family of the church", the Archbishop notes.
And it's not just for royal babies but all babies.
"God's love is offered without qualification, without price, without cost, to all people, in all circumstances, always," the Archbishop says.
Explaining what will happen when he baptises Prince George, he says: "I will mark Prince George with the sign of the cross on his forehead, and that's exactly what every single priest does at every single baptism. It's an extraordinary moment because that is the sign by which we understand that this person belongs to God."