That doesn't work very well on a humid day outside in the summer.
And the payphones in the city I grew up in didn't operate using ground-start signalling, so the paper clip/safety pin/pull-tab/static trick didn't work there at all.
But an innocuous walkman with a cassette tape that had some red box tones on it, with a bonus of having the rest of the cassette available for music to listen to? That worked great.