In the upper right, click on your name, and then select Account & Billing
In the Subscription Info area, click on the button below.
Then click the box next to Additional 1000 SMS. Please note that you are able to determine how many SMS messages you would like available monthly by increasing the number under Quantity. The price is $15 per month per 1000 messages. For instance if you place a 3 in the quantity box, you would receive 3000 messages for $45 per month
