I think you can only be in Sinnoh, which is a shame.
No you cannot go to other regions in Pokemon Pearl or Diamond version but in Pokemon Heart Gold and Soul Silver you can go to the Jotoh region.
The entirety of Pokemon Pearl and Diamond is set in the Sinnoh region. There is no way to revisit any of the other Pokemon world regions.
because they want get out of there country
You cannot go underground as you were able to in Pokemon Diamond and Pearl. You are stuck above ground in Pokemon SoulSilver. You get two regions to go between, though.
Unfortunantly you cant go to other regions in Pokemon diamond and pearl. its not like leafgreen,firered,gold,silver and crystal version where you travel to different regions. You can't, Sinnoh is the only region available in the game.
It is only in HeartGold & SoulSilver and Gold & Silver you can go to different regions :/(and Crystal)
No.
After you see all the Sinnoh Region Pokemon, go to the Professor, and he will give you the National Pokedex, which includes Pokemon from the Kanto, Hoenn, and Johto Regions.
No but you can catch many of the Pokemon in Sinnoh after you beat the Elite 4
You can get the Pokemon in Sinnoh. If you go to Pokemon.com, you can see them.
You can go on gamespot.co.UK and search for Pokemon pearl
When you receive it, go play Pokemon Pearl and go to the pokemart.