I would say if you are always hitting five days a month, you should probably just get one of the dedicated data plans with any of the majors. They run $60 a month for 5 gb of data. Either tie that in with a usb modem or a mifi router from Verizon or Sprint and you may save some money.
If you have a corporate discount with verizon for the voice they may be able to extend that to the data line too saving you a few pennies.
Verizon offers pay as you go, $15 a day for 75 megs of data, $30 a week for up to 250 meg of data, or $50 for a month and up to 500 megs of data.
http://www.verizonwireless.com/b2c/m...ucts_prepaidmb