"Best app by far" ☆☆☆☆☆
Just downloaded this and even at just a small look I was impressed. Well worth it. Buy it (USA)

"Excellent" ☆☆☆☆☆
..I have been using Eirtext Pro up to now and have switched over to Jelly SMS and won't be turning back! (Ireland)

Jelly SMS ( JSMS ) allows you to send free or very cheap international SMS text messages from your iPhone or iPod Touch!

Features:
- Send messages to any number in your address book. Select contacts as you would in the native SMS app.
- 'SMS My Location' feature which lets you send your current location by SMS.
- Set the default country code so you don't have to place it into each number manually each time.
- Forward SMS sent by Jelly SMS
- Send to multiple recipients at once
- Get replies direct to your mobile (register number on the provider website first)
- Landscape SMS typing and more..

All you need is a free account with any of these providers:

Clickatell Central (clickatell.com)
O2 ...