To view the usage for your Mifi unit you can dial #3282 (#DATA) from a Verizon Wireless handset.
#DATA will provide you with the information for the number you are calling from, in addition to any other number you would like to check (i.e. The MiFi unit). After the recording has read the options for the number you were calling from, just press option 4 to check another lines usage (like the MiFi). You will receive a text message for the line you were calling from usage, however a text message will not be sent for the MiFi usage number.
I hope this information was helpful.