Hi Chandra. I looked at indoor positioning last year and it's not quite as developed as one would hope - especially on iOS because of highly-restrictive Apple policies on wifi scanning. Most vendors seem to require professional services to implement (Meridian, Wifarer, etc.) and I'd be wary of creating dependence on relatively expensive technologies that will undoubtedly be built into Android and iOS within a year.
Apple just bought wifislam which had a good Android solution (~ 3 meter resolution) and were working on an iOS solution (~ 5 meter resolution) but I'm sure (a) Android version will get killed, (b) iOS version will get a lot better and (c) it'll find its way into iOS7 (maybe 90% sure on this one).
Clearly with the acquisition, Apple isn't going to relax their restrictions. There are other approaches but most of them require the site to adopt hardware (e.g., lighting systems) and that's a slog.
Soooooo, it really depends how time-critical this is to you and how much precision you really need. 20 feet is kind of between GPS and IPS... can you get by with GPS inside of airports which assumedly have good coverage? Do your own analysis, but my gut tells me that by the time you actually integrated an existing solution (at significant cost), you'll see it baked into the os/devices.
As an aside, I spent a ton of time thinking (and some implementing) location-based offer systems... I'd be happy to give you a brain dump.
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