For the next few days, you can send a message to E.T. for free.

Specifically, you can send a text message to Gliese 581d and say "Hey."  Never heard of that planet?  The HelloFrom Earth website explains that it is
"a super-Earth about eight times heavier than our own planet. Gliese 581d and its three known sister planets orbit the low-mass red dwarf star Gliese 581, about 20.3 light-years (194 trillion km) away from us, in the constellation Libra."  Who knew?

The project, a celebration of National Science Week in Australia, will gather up messages to be sent en masse after the collection of texts ends on August 24, via the NASA Jet Propulsion Labs. The data will be reduced to a binary transmission and returned to the NASA/CSIRO Canberra Deep Space Communication Complex at Tidbinbilla, near Canberra to be sent on its way.

But don't expect an answer right away.

Because of the more than 20 light-years the signal will have to travel, it is expected that the messages won't arrive at their destination before December 2029. If the messages are received and understood, a reply would take the same amount of time to return. (Unless they just sent a superstellar bomb to wipe out the planet because humans are too dangerous.)

However, not just anyone will be authorized to reply to the aliens who may contact us. "If any aliens respond, Earth protocol steps in.
Response to any non-human communication received from another planet needs to be coordinated by the SETI Post-Detection Taskgroup of the International Academy of Astronautics, chaired by Paul Davies," the website warns.

Reading over the list of nearly 6,000 messages gathered so far, it's not certain aliens will even want to bother with people on our home planet:

Luke from Brisbane, is practicing Obama diplomacy:
I'd like to invite you all back to my place for a few beers.

Kay from Adelaide: Have you seen Dr Who? He seems to have left our TV screens. Please send him back (preferably in the form of David Tennant!)

Colin from Melbourne: Greetings from Earth. About 2,000 years ago the Son of God Himself visited us and we crucified Him. So I suggest you stay away. Regards, Earthling.

Victor from Venezuela: When you come here make sure you get a copy of all Britney Spears albums, you're going to love them.

Joshua in Charleston, US, offers different encouragement: Come visit us here on the Earth, we will share peanut butter, heavy metal music, and chocolate ice cream!

There are many offers of beer, and about an equal number mentioning chocolate as one of the highest achievements of Earth creatures, in among more spiritual and scientific remarks.

To add your message, which must be more than ten characters but less than 161 characters, in English (can Gliesians read English?), and not offensive, go to the registration site before August 24, 2009, and secure your chance to speak to someone from another planet.