um....well,I'm not very familiar with Taiwanese' tones,yet I know the phonetics are similar...I guess difference does exist,since you know,a strait lays there between mainland and Taiwan,this can definitely cause some difference,in mainland,we pronounce朋友as"peng2you3"....Anyway,we can still understand each other,and it's OK to speak either way.But I still think that the pronunciation and tones of Beijing mandarin is more standard and correct than Mandarin in Taiwan...since you know,Northern China is the cradle of Mandarin and ancient Chinese civilization.....hope this can help ya..:D