Nokia (NOK) has started pricing the Lumia 620 in Asia nearly 20% below the rival Windows mid-market model, the HTC (2498) 8S. This is remarkably aggressive considering the 620 has a higher pixel density and twice as much internal memory. The 620 is the keystone phone for Nokia. It is launching before RIM (RIMM) gets its new budget BlackBerry phones out and before Samsung (005930) or LG (066570) enter the mid-priced Windows phone market. This is the phone that will make or break Nokia’s summer.

Nokia has started rolling out the Lumia 620 in several key Asian markets by the third week of January. It now looks like its European debut could happen a few weeks earlier than expected, perhaps by the end of January. In one of the earliest launch markets, Thailand, the launch price of the Lumia 620 is set at 8,250 baht, or $275. The only direct Windows mid-range model, HTC’s 8S, is priced at 9,990 baht. The Lumia 620 is priced at 800 RM ($266) in Malaysia, one of Asia’s key mobile markets. HTC’s 8S launched in Malaysia at 999 RM.

Nokia is the stronger brand in South-East Asia and HTC’s budget Windows model was expected to be at rough price parity during the 620 launch, not 20% above. Nokia’s Lumia 620 features display pixel density of 246 pixels per inch, a touch above the 233 pixels per inch that HTC’s 8S offers. The 620 also packs 8 GB of internal memory, twice as much as the 8S. Camera and video quality are roughly similar.

This is the golden opportunity for Nokia. It will probably take at least until June before RIM rolls out new BlackBerries priced under $300 in Asia; possibly late summer or autumn. Samsung and LG are a step behind Nokia in rolling out their Windows Phone 8 ranges. HTC’s first mid-range model doesn’t quite measure up to the 620 in value for money comparison. Apple’s (AAPL) rumored cheap iPhone is unlikely to arrive before September.

Nokia now has a shot at recapturing some of the power it used to have in the mid-range smartphone market. Back in 2006 through 2008 Nokia dominated the smartphone markets of Asia and Europe with absolute sovereignty, capturing market shares as high as 70% from India to Germany. Those days won’t return, but if the 620 clicks, Nokia just might have a shot at pumping the Lumia volume to 10 million units per quarter by autumn.

The relative market softness in the sub-$300 category due to the current weakness of RIM, LG, Sony (SNE) and HTC has opened the door. This February is going to be an absolutely crucial month for Nokia as it ramps up its most important Lumia phone during the traditionally dead period in Asia and Europe. If consumers don’t connect with this model at this price, the entire Windows Phone camp will face some very tough decisions.