This is true to a limited extent. But please don't interpret this as meaning 'There is no difference between the "I've worked" and "I worked". There IS a difference in most cases, it is important to use these forms correctly. In a few situations, especially in US English, the two forms may be used interchangeably. For example, if you lose your keys and then find them, you could say 'I found my keys' or 'I've found my keys', and the meaning would be the same. US English speakers tend to use the past simple in this situation whereas British English tends to use the present perfect. And while a British English speaker would always use the present perfect with 'yet' and 'already', a US speaker might make no distinction between 'I already had breakfast' and 'I've already had breakfast'.

However, the two forms are NOT interchangeable in all situations. Please do not take this as a licence to throw away your grammar book and think that the distinctions don't matter. In most cases, they matter very much.

For example:

'I worked in New York last year' = correct

'I've worked in New York last year' = incorrect

'I've worked in this company since 2005' = correct

'I worked in this company since 2005' = incorrect

Or how about:

'I worked for Samsung for 12 years' and 'I've worked for Samsung for 12 years' ?

They're both correct, so they have the same meaning, right? Wrong. These two sentences have completely different meanings. 'I worked for Samsung for 12 years' is past simple, indicating a finished period of time. This means that you don't work for this company any more. 'I've worked for Samsung for 12 years' is present perfect, indicating an unfinished period of time. This means that you are still employed by this company now.

So, as you can see - the choice of tense is sometimes very important indeed.

I think in casual conversation that the past tense and the present perfect such as: "I worked" and "I've worked" are often used interchangeably (the same).  However, "I've been working" suggests an action that happened in the past and is still happening.  If you were in a job interview, that would be an important distinction!  

It heavily depends on the context and on the message you want to address.

for example, in a job interview, it would sound better and effective if you say "I have worked since... or for..." because here you are trying to emphazise on the expereince that you have gained from that particular job and on the length of the working duration.

Otherwise, if there is no particular empasis on expereince, influence, interruption acttion or duration I think "I worked and I have worked" both are coorect.

I hope that helps you.

cheers

Thanks Koala and Mary!

spelling hihi not again.