Quick and dirty:
Assume that on the turn, you win if you hit your gutshot. 3 outs. 47 cards to come. 6.4% chance of hitting on the turn. The pot is laying you 9.5:1 which means you have a 9.5% chance to win. However, I think a safe assumption is that you will get at least 2 more BBs out of UTG due to his PF raise and lead on flop, so the implied odds mean the pot is laying you 13.5:1 or 6.9%.
With these assumptions it's a close fold. However, if you think you can get another BB out of someone on the turn or river, then the pot is laying 15.1:1 or 6% and you can call. Plus, you have the back-door flush which may be good if it hits. However, there will be instances where button has a 7 and you will end up splitting the pot so you can prolly figure you have right around 3 outs at the moment.
I think you can assume here that you can get 3 more BBs out of someone on the turn and the river, so I would make this call. If this call is a mistake, I think it's a small one.
Let's do the turn:
The pot is laying you 6.75:1. Let's assume you'll get one more BB out of UTG on the river, so the pot is really laying you 7.75:1. You now have a flush draw. This time, let's put UTG on a hand range and use pokerstove (
www.pokerstove.com) to figure our equity. Since UTG is TAG, let's put him on 99-AA, and AK-AQ and AJs.
With UTG's range you have 31% equity. Very nice. 7.75:1 is 11.5%, so the turn is a much easier call than the river.
Well played.
Edited to add: On the river, even if we assume UTG already has a pair higher than a seven, you still have 21% equity and should call.