If your 'unlimited plan from Walmart' is Straight Talk - it is a violation of their Terms of Service to use 'tethering' or 'hotspot' functions:
STRAIGHT TALK UNLIMITED PLANS CANNOT BE USED FOR: ANY APPLICATIONS THAT TETHER YOUR DEVICE TO A LAPTOP OR PERSONAL COMPUTER OTHER THAN FOR THE USE OF WIRELESS SYNC.
While Straight Talk does offer their own 'hotspot' devices - there is nothing unlimited about them - you pay by the GB used.
If you get their attention with your data use - people have reported data restrictions up to service termination (phone rendered useless, number lost, and remaining time lost). Use at your own risk...
(Of course if it's not Straight Talk - and the provider allows it - watch all you want...