GBA sold about 16.7 million in Japan. PSP is currently at 14.51 million and last year it sold 2.4 million. This year PSP has sold about 800k units in Japan so far so if we assume that it will do same kind of numbers as last year PSP's LTD sales in Japan will be 16.1 million when this year ends and so the gap will be about 600k units. PSP will sell that much next year even with release of PSP2.
It's at 16,960,000 shipped lifetime. More surprising is that it only did about 1.48m of that after DS launch, meaning a staggering 15,480,000 in just over 3 and a half years.
PSP will beat it, but only by virtue of being on shelves longer. After 3.5 years it had shipped only about half what GBA did in the same period.