No, you can access the PTAsocial web app from any internet browser, e.g. on your desktop computer. PTAsocial is designed in a responsive way, so it will look good on any device. Smartphones are particularly handy because they conveniently allow browsing and volunteering on the go, even in the school playground.
Please note however that Internet Explorer 8 users will not be able to use some important aspects of the app, like creating private messages. We recommend upgrading to Internet Explorer 11, or switching altogether to Chrome or Safari, which can be downloaded for free.