You can download the latest MobileVOIP app directly from this page, if you can't access the market. You will also find the previous versions of each application here.
Google Play 8.24
Google Play 7.41
Google Play 6.92
Google Play 6.50
Google Play 5.88
Google Play 5.84
Google Play 5.79
Google Play 5.26 (supports Android 4.x and up)
Google Play 4.63
Google Play 4.62
Google Play 4.51
Google Play 4.47