All Pro accounts are given 25 free SMS per month as part of your subscription. If you require more, you can purchase credit in bundles of 25, 50, 100 and 200 – and the price works out as £0.05 or(US$0.07) per message.

To purchase extra SMS credit

Under Settings on the main, left-hand navigation, select SMS Credits. This will take you to a page showing how many credits you currently have, as well as your SMS Invoice History and Recent SMS Messages.

Click on Top up your credit, select how many credits you would like to buy, and Continue to payment.
On the next page, enter in your payment details and your billing address, and hit Purchase.

NB: Payment will be taken instantly from your chosen payment type.