This is the reason the 600Mhz processor in your phone will have worse performance than a normal 600Mhz processor. Mhz is useless as a measure for performance and it became popular only because of marketing campaigns by Intel, when they had an edge in the Mhz race. A more useful measure (other than running unbiased benchmarks) would be MIPS (millions of instructions per second) and MFLOPS (millions of floating-point instructions per second).

For example an ARM11 from 2002 at 412 MHz was able of 515 MIPS (millions instructions per second), while a Pentium Pro from 1996 was capable of 541 MIPS at 200 MHz. Also an Intel Core i7 EE is capable of 177,730 MIPS at 3.33 GHz, while an AMD Phenom 2 X6 from 2010 is capable of 78,440 MIPS at 3.3 GHz.

Basically your 600Mhz mobile processor is not the same processor you had when playing Counter-Strike a couple of years ago. That's because it is optimized for consumption rather than performance.