How many and what processors are used in a cellphone and a PDA?

Dear all,

Is one ARM processor enough for a PDA?Or it needs both DSP and ARM?

How many processors are usually used in the current cellphone?DSP or ARM or both of them?

For a video cellphone, how many and what kinds of processors are usually required?

I am curious about the computation capability of ARM and DSP processors.

Thanks,

Adrian