number vs non number makes no difference whatsoever in regards to using the voicemail features........ IMO theres no reason NOT to get a number if one is available in your local calling area...... that is to say EVERY feature available without a GV number is also available with a GV number...... the opposite is not true
as far as texting goes..... its my understanding you would need to have a google number in order to take advantage of free texting.... with the way that it operates
you need the GV client on your phone (available in the Market for free)..... when you want to sent a text you just open the client and send from there......this text will appear to come From your GV number on the receiving end.......... in order to receive free texts then you need to go to the online GV website and under settings>voicemail and text> select Forward text messages to Email....
this way when someone sends a text message to your GV number it is forward to your Email instead of being sent to your phone directly (this eliminates any text charges from Verizon)........
summarized: you send txt from the GV client on your phone... you receive txt through the email client on your phone....... yes its a little more tedious process....... but its completely free this way and you can save the $$ from whatever texting plan you have with Verizon
of course I only casually use GV so if anyone has different theories or thoughts feel free to correct me