I don't have an AIM account and don't want to set one up just to test so perhaps someone who has AIM can see if this works to SpeakOut and/or PetroCan Mobility:
Send Text Messages for Free via Instant Messenger
You can send text messages to many cell phones via AOL Instant Messenger.
To send a text message via AIM, simply message the telephone number. Include a plus sign and the country code. For example, to text message your friend at (303)555-1212, send an IM to +13035551212.
From http://www.tech-faq.com/send-t…..free.shtml which also includes Send Text Messages for Free via E-mail to cellphone subscribers in a variety of countries.