One of the text message utilities I have been using for years is Teleflip.  Rather than waste my money on text messaging friends and colleagues from my cell phone.  I use this service.  I find it much faster to type out a quick email to them than screwing around with the keys on my phone.  Just click on the image below to try out Teleflip.

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Another cool thing you can do with Teleflip is enter in the cell number you want to contact into your email.  I find this a lot more beneficial than going to their website every time.  You just need to type in 1(555)-555-1234@telefip.com and send the text message on its way.  Then you can save that contact to easily text message your contacts from email.  *Note I have only tried this with my Yahoo Email account and it works, so I cannot speak for any other services.  If you have information on other services definitely share them with us!