WiFi is a local communication service. Voice is a paid network feature. Data (3G/4G LTE) is also a paid network feature. All three services are different and are not dependant on eachother. Jetpacks can operate as an independent WiFi Access Point for your local personal computers without an active VZW account.
If you want the Jetpack to provide a data connection to the VZW network then you need to activate an account with VZW.
> I dont understand why it has a number or how i would recive a call off of it
All VZW devices have phone numbers associated with them.
This is the result of Jetpack technology and how its based on cellular phone technologies which are dependent on traditional phone numbers. Thus, if you want to access the VZW data network then your device needs a VZW phone number to "dial into" that network and authenticate. Your Jetpack is essentially a cell phone that is modified to provide data only services. Many Jetpacks can even receive text messages and voicemails, although there is no way for you to respond to them. Most people disable voice and text on their VZW account for Jetpacks to avoid additional fees.