That's an old news story prediction from July 2006.There are many tech sites that have such story's and they turn out inaccurate but sometimes close.
Generally AM3 processors are backwards compatible with AM2+ motherboards if there is a CPU BIOS update for it.
You do not have a AM2+ motherboard you have an earlier AM2 motherboard.
The motherboard that you have is a nForce 520 based Abit AN52S like you state.
Here are the list of supported CPU's for that old board.
http://www.abit.com.tw/cpu-support-list/mb/nv_nforce520_an52s.htm
The most powerful CPU as listed here is the old Windsor Athlon 64 X2 6400+
Hard to find except for in used condition ( a seller who might have upgraded his CPU for a more powerful one).
I do see a m701a16 BIOS listed as of "Bios Issue Date:2008/06/30"
which states
" 1. Update CPU Micro code to support Phenom CPU and Athlon 4X50 series and Sempron X2 CPU. (The S3 return fails when used Phenom CPU, this issue is chipset issue.)
2. BIOS compiled date: 06/30/2008."
So perhaps it is possible to use the earlier Phenom (1) series on this motherboard.
http://www.abit.com.tw/page/en/download/download_bios_detail.php?pFILE_TYPE=Bios&fSEARCH=Search&fSEARCHTEXT=AN52S
You might want to download this and read the text file as it may mention the type of Phenom CPU that can be used with this BIOS.Though you may have a hard time finding an older Phenom as well.The B2 stepping of the Phenom had the TLB bug and the B3 stepping corrected this.