From a 14.3% share of the global market in September to a 20.3% share in December

Click to enlarge. Estimates: Canaccord. Chart: PED

A note to clients issued Tuesday by Canaccord Genuity’s T. Michael Walkley had good news and bad news for Apple AAPL investors.

The bad news, which we reported here, was that he expects sales of Amazon’s AMZN Kindle Fire to cut sharply into the iPad’s dominance of the worldwide market for tablet computers, reducing its unit share from 74% in calendar Q3 to 53.2% in Q4. (This is not such bad news, Apple execs told J.P. Morgan last week, because they expect the $199 tablet that Amazon sells at a loss to whet consumer appetites for the iPad, which Apple sells at a tidy profit.)

The good news in Walkley’s note is that he is seeing “strong global share gains” for the iPhone versus Google’s GOOG Android this quarter — strong enough for him to increase his iPhone unit sales estimate for Q4 from 29 million to 30.5 million.

The change is even more dramatic when you consider that Apple sold only 17.1 million iPhones in the quarter that ended in September.

The pie charts above show what the smartphone market looked like in Q3 and what Walkley expects it to look like at the end of December. (We’ve copied his data below the fold.) In addition to Apple’s 6 point (42%) increase in market share, note the double-digit share drops among its competitors, including:

HTC, down 4.3 points (39%)
Nokia  NOK , down 2.4 points (17%)
Sony Ericsson  SNE , down 0.6 points (11%)

Samsung is basically holding steady this quarter, according to Walkley’s forecast, shipping an estimated 34.5 million smartphones but losing 1.3% of its market share.

See the spreadsheet below.

Click to enlarge.