yaxim (Yet Another XMPP Instant Messenger) is an XMPP client with a clean user interface and open source (GPLv2). Why pay for SMS if you can have unlimited messaging on your data plan?
yaxim aims at security, low overhead and keeping your server connection open. So far, it only supports a single account.
* Connection with a single XMPP server (or GTalk, or Facebook Chat, or …)
* Immediate reconnection on 3G/WiFi network changes (seamless with XEP-0198)
* You are asked about self-signed SSL certificates
* Allows automatic connection after turning on your phone
* Roster management support
* Persistent message history
* Message Carbons (XEP-0280)
yaxim is optimized to use the yax.im free XMPP service: http://yaxim.org/yax.im/