Actually, in speech, you might hear a sentence like "I been working here 10 years" (instead of "I've been working...") both from uneducated speakers and from highly-educated speakers.
The difference is that an educated person KNOWS (mentally) that the contracted auxiliary verb 've is there in the sentence; he's simply being careless about his pronunciation, so that the 've becomes silent.
But a poorly educated speaker may actually believe that "I been working..." is the correct form.
And thus, in written representations of speech, "I been working..." may be used to show that a person is uneducated, or it may show that an educated person is (for example) drunk, and therefore not pronouncing his words carefully.