Scenario 1: Let's assume 100 persons do both smartphone and post cards. Once they has voted, the poll says 100 votes for smartphones and 100 votes for post cards.
Scenario 2: Let's assume 100 persons do smartphones only and another 100 persons do post cards only. Once everybody has voted the poll says 100 votes for smartphones and 100 votes for post cards.
However the 2 scenarios are drastically different.
Then the poll says how many members have voted - and that will add to the understanding - but with multiple choices (GPS Tracking, pay phones etc) the overwiev is lost.
Basically the main objective of the poll is to see how many have adopted the electronic gadget world compared to the more "snail mail" world. This why, I suggest voting for the preferred method (as in the original posting). I know, this is not perfect, but it is to ensure that each vote is from a unique, single user. You can do a poll with multiple choices, but then it becomes excessively large.