Question. Will using a vpn on a cellie do anything to mask my transactions? For that matter, does it on a regular pc?
More details would help but on first instance yes, it would help... As soon as there is nothing that can associate you with that VPN (ie: you pay with credit card, etc). The VPN provider would of course see all the traffic you route through them.
Cellphone/PC is almost the same in this case. Also take into account that there are additional ways to fingerprint devices or identify you if you use that same VPN for other things (such as web browsing).
For a "one-time-hit" it would be better to use a free wifi somewhere (without cameras around) with a clean OS (TAILS may be a good choice here) and custom WIFI MAC. Expect your traffic to be captured... but it is assoting with your person what you were worried about, didn't you?