You can use Group.Me on phones, tablet or your computer but they work a bit differently on each. You can download the app on your phone, signup online or if you just want SMS, ask to be invited into a group. At its core Group.Me allows you to connect and communicate with a group via SMS (text messaging). It has more robust features if you install the app on your phone or tablet or log in from a computer. Regardless of where you decide to engage with Group.Me you will be able to send and receive messages, either via SMS, the app or online to anyone else in the group, regardless of how they opt to connect.
There is no charge for the app, but it will use SMS or data depending on how you connect with a phone.
You can invite people either via SMS or email to join a group. One caveat, if you enter by SMS and then later install the app, you will receive both messages in the app and SMS (you have to turn this by logging in via browser to change the setting).