The English language version of Wikipedia has over one million articles and many of those relate to objects which have a geographical location [e.g an historic building]. It would be useful if you could read the Wikipedia article for a location on your mobile phone [or other device] when you were actually there. Or, find find locations near you which have articles about them.
The first step in making this possible would be to tag locations. This could be done by means of a physical tag, such as a QR code. If your phone had a camera you could point the camera at a code fixed to a building and your phone would read the URL in the tag and call up the places Wikipedia article in your camera's browser.
An alternative approach uses virtual tags. Many Wikipedia articles have already been geotagged. If your phone had a GPS device it could connect to the Wikipedia database and search for any article with a GPS location close to your current location.
Both approaches are now possible on modern phones. All that is needed is the phone's GPS/camera and some extra software.
Apple have opened an Apps Store to allow third party developers to create applications for the iPhone/Touch. Somebody has created an application called WikiMe which allows you to detect virtually tagged articles near you and call up their Wikipedia articles.
You can find WikiMe on Itunes/iTunes Store/Apps Store. The images below which give you an idea of how it works.
There are a lot more geotagged Wikipedia articles than there are places with physical tags on them. One of the problems with physical tags is that they are usually small and hard to find, though they are more precise. For example, you could geotag a museum, but physically tag individual exhibits. Another problem is the absence of a standard for physical tags. At the moment there are too many different code formats [e.g. shotcodes, semacodes, barcodes and QR codes].
Geotags also have their limitations. They are easier to create and more flexible than physical tags but it can be difficult to get accurate GPS readings in a city. This is due to change when the EU's Galileo satellites are in position.
Of course, you can link to more than Wikipedia articles. You can hyperlink any object in the real world. Companies can create web pages and tag them to promote their products. That is already happening. Companies could also create informative pages about locations and charge people a small fee to read them. It has proved hard to implement micropayments on the internet because there is no effective charging mechanism. However, the phone system does have a charging mechanism and it would be easy to charge people a small amount for reading a useful page.
If you have the software in your phone's camera to read barcodes you can even do price comparisons. Just read the barcode on a product and then check if anybody nearby is offering it at a lower price. Once you have phones with cameras and GPS chips, and a system of tags all kinds of things become possible.
Hyperlinking the real world