Google voice also does not require a resident app on your phone. Simply use your phone's browser to access the GV mobile web app at
www.google.com/voice and it will automaticly present you with a trimmed down mobile device webpage. Logout, clear your browser history, and your phone is clean for anyone else to use. Expecting a call via your GV number? Go into settings, select forward to your cell, and then texts and calls will forward to your cell, but they will come from a Google Voice trunk line, not the actual originating phone number.
NOTE: If you install the GV app on your phone, do not let it upload your existing contacts. Keep your real world contacts on your phone ONLY. Keep your hobby contacts in your GV account ONLY. If you have a Google or GMail account already for the real world, DO NOT CREATE YOUR Voice account from there. Create a new Google Account for the hobby GV number.