Credit on your Vodafone Card is active always for a period of 10 months after last charging or after buying, if you haven't charged.
The initial Extra Credit is valid for 45 days from SIM activation and you can use it for Vodafone services (you cannot pay for third party services such as SMS tickets).
After your credit expires, you still have a three-month period to renew your Vodafone Card.
If you don't recharge your credit during this period, your phone number will be automatically cancelled.