Basically, Central Thai is spoken all over Thailand, so you can go anywhere in the country with it. However, people of other regions (southern, northeastern or Isaan, for example) might have a slight accent when speaking Central Thai to you, but you guys will be able to communicate in Central Thai with no problem. :) The local people also have their own dialects too though, which they normally use to communicate with each other. If you're speaking with a southerner, words from their dialect or their unique slangs might slip into the Central Thai dialogue at times. But this shouldn't pose too much difficulty. Just ask if you don't understand something, we're very friendly people! :) good luck in learning Thai ka.

yep, if you speak central they can understand :)

khop khun mahk khap.. ^^ so if i speak central dialect to the southern ppl, they can understand?

yes, it's difference but you can use central thai. it's dialect.

Example : http://www.ipesp.ac.th/learning/thai/chapter4-6.html