If you mean HSPA+ then the Nexus One doesn't have the same radio to pick up the full frequency. If you want the 4g type speeds of 7.2 mbps - theoretical 21 mbps then the G2 will do it for you (granted you living in a HSPA+ area). I live in southern california and currently get around 3.5 mbps download and 1.5 upload on my Nexus One w/ T-mobile which is more than enough.

 

I thought that I read somewhere that the HSPA+ also benefits regular 3G phones with better download speeds.
Either way, my friend just got a new G2 and while I was with him the other day I had both of our phones run the speed test app and I had a faster download speed all 3 of the times I tried it. My phone was on 3G and his displayed the H for HSPA.

 

The N-1 will benefit from it but the newer phones will be better equipped to take advantage of it. I have the "H" here in the Tampa Bay Area.

 

You have the H on your Nexus One in the Tampa Area? Are you running a custom ROM? Because I'm in the Tampa Area and I've never seen an H on my phone.

 

Cyanogen 6 but even on stock 2.2 I had it. I am usually in Brandon/Tampa and get it consistently. It's a nice little bump in speed.

 

I get around 4.5-4.7 / 1.3-1.4 mbps in So Cal although I don't get that everywhere.

 

The H from Cyanogen 6 means you are getting high speeds (as high as the phone could get) but your Nexus One will still not benefit from 4g speeds/T-mo software update.
Cyanogen doesn't 'unleash' new speeds, it just shows where 3g speeds are maximized.

For 4g speeds, check out the new Mytouch 4g which is the first phone that could compare to our N1 in my opinion...

 

You may or may not see a bump up in speed, depends on what you were getting before. I live in a HSPA+ area and my speeds are all over the place. Sometimes I see below 1mbps, sometimes it jumps up around 4mbps but usually it is around 1.6mbps.... which is what it was before it was turned on here. :S