What I would suggest is that you add a counter to each row of that dataset - you will also need to ensure your dates are formatted correctly. This inline statement should give an idea:
1 as PhoneCount,
date(date#(Date, 'DD MMM YYYY'), 'DD MMM YYYY') as Date
iPhone,1 Jan 2011
Android,24 Mar 2011
With the data in this format you can create a combo chart. Set the Date as the dimension for the chart. Set the first Expression to be sum(PhoneCount) and select that to be a symbol. Put a second Expression in simply of Phone - set this to be Values On Data Points. You will also want to check that you have a Continuous axis.
This should give you something to start with, I would sugest you want to also want to play about with the formatting. The attached .qvw file should give some ideas.
Hope that helps.
Timeline.qvw.zip 113.5 K