- Why you can't do this
This can't be done, for the simple reason that mobile phone network operators put measures in place to ensure that all of their networks are secure and that nobody would be able to do something like this. Not only that, if you were even able to do this in the first place then you would be breaking the law. You would be using the network provider's network for your own use without paying them the fee that is required. Using the network requires the contract between you and the provider, which involves a transaction of money.
- Ways to talk and text for free
Many network operators offer schemes that allow you to get 'free minutes' or 'free texts'. A lot of operators will provide you with gifts like this if you top up a certain amount on your prepaid phone every month. If you stick to these deals then you will be given free minutes and free texts by the network operator, and you won't have to do anything else but keep up the payments. This is really the only way that you're going to be able to talk for free on a prepaid Verizon phone, unless you're going to reverse call people - which is obviously not always feasible.
- Other options
You could always obtain some kind of mobile device that supports 3G connections. By doing this you can then use free software like Skype that allows you to talk to other people using the same software for free. This would mean you would only have to pay for the Internet connection and not for the chatting and texting functions that you'll then be able to install onto the device.