This plugin stores tokens from apps used for push notifications. It creates an api endpoint which your app can send tokens to and also supports a key
Send SMS via Bongolive services in wordpress
Send SMS via wordpress
XMPP sender allows to send (and receive) notifications about new comments in blog. Also it can override email function to xmpp for your blog.
Allow visitors to e-mail themselves the URL of the current page.
dont_send_mail does't let wordpress-mu send mail at all.
Send an email (subject and text message) to WordPress users.
Plugin that enables you to send e-mails quickly from your wordpress.
Plugin for sharing wordpress posts into WPDelicious.
Configure a mail server you want to use for mailing in WordPress