Picture this scenario.  Worker is out in the field with no phone connectitiy and needs to have a client confirm a sale with a signature.  We have to let the sale happen and then make ture the sale goes to the online database as soon as the connection is back up.   The other is when you wish an applet for apple/google/windows store.  There is similar setup, but the client is going to download the app to the phone and use it to access from anywhere.  This causes the app to keep the data up to date by accessing the data in the tables on the web.  The data base on web can be sql with php, java or whatever, but the generally accepted database for the phone is sqlite and it usually runs with javascript and or jquery.

Phone apps/applets usually start in price from...$10,000 and generally wind up at around $20,000.00 for a real good one.  Sounds like a lot, and it is unless you are able to sell the use of the applet for 1.99 each times a few million copies.  Look at this from cnn and tell me?   www.cnn.com/