For anyone interested I contacted UNMAS regarding this and got a very nice response:

This is a Response to your query. It is a technical outline of shortcomings. And is only meant for you.

This is a very developed world approach to a developing world problem. The main reasons for not investing heavily in such a system are:

The requirement for a 3G network.

The issue of how to verify reports

The problem of false positives

The problem of false negatives

The potential for it to guide the foolhardy onto problems rather than away from them

The simple fact is that Joe/Amy Public does not need this sort of info at the micro level. It is reasonable to warn the public and humanitarians at the village level (i.e. the village is safe or dangerous, not specify that there is known contamination at 23 Acacia Avenue, because there may well be additional unknown contamination at 27 Marlborough Drive). There is then the problem of updating such system in response to the positive actions of mine action organizations, which would generally be logged and tracked, but there would be no accounting for the acts of local heros who "helpfully" move things to less obvious locations.

That is an idea of the shortcomings of trying to design and maintain such a database. Very locally – and with signage and warning tape, mine action organizations are doing this, but maintaining and ensuring a database is correct, is not easy.

Thank you for reaching out.