I live in Argentina and we don't have the Bachelor/Master's division. I've studied 6 years of a Biology Degree. Most of my subjects had Lab practices besides the theory/calculus part so my total amount of college was big (a normal subject would have 12 hours/week with a total of 23 subjects). Within the 23 subjects, we have 13 "general to all Biologists" and there are 9 which are "specialization" subjects. Then, if you're going for "neuroscience and behavior" you have to attend "Neuroscience 101" and you can't go for "Plant Vascular System 4". Also, in order to graduate I have to have research experience and present a written "thesis" (and give an oral presentation) which is consider your last subject. I've worked for two years in a Lab doing this research. Because I want to do my PhD abroad I'm wondering if there's a way to explain this or have some kind of equivalence. Since there are lots of automatic systems that are ready for you to complete Bachelor + Master I find a lot of trouble to deal with this. I feel that it's too difficult to get to talk to a real person and when you actually do, the person gives you the "go to the website and..." Any experience will help (specially if you had the same problem and you found the way to deal with it).
You are in a slightly tight but not an impossible to overcome situation.
What you describe relates very closely to the pre-Bologna_Process situation in Europe. People especially in Science- and Engineering-related disciplines had 5 to 6 years Bachelors (usually called Diplomas). When these graduates applied for graduate studies, especially in UK where the BSc in usually 3 years, they found themselves massively downplaying their qualifications. (The situation is somewhat sorted now.) Currently the old diplomas are almost universally accepted as Masters degrees because the retroactively calculation of ECTS points puts them nearly always in the same range as a Masters degree.
When you say abroad you do not specify where.
If abroad translates to Europe then things are quite straightforward. You say you have a Masters and leave things be. Departments are quite used to the phenomenon of "5/6 years of studies". Most of admissions committees will not blink an eye. It would almost certainty good to present it in your CV as "Integrated BSc and MSc studies" or something equivalent, so one can immediately spot it. Your programme of studies is far from unheard in Europe.
If abroad translates to US/Canada I do not have personal experiences; I think it will greatly dependent to the particular university's guideline. (I will be happy to be corrected at this point from a North American native if there is some standardised framework I do not know of). I can tell you for sure that 4-year BSc are not counted as Masters. I know very few people who applied for PhD straight out of a 5-year Engineering degrees from Greece; both them were accepted but they were very strong students anyway so I would not extrapolate based on them. Some others went for Masters (and continued to PhD eventually).
In general, a 6-years degree puts you in a very strong position if you are to be compared with simple BSc holder for PhD admission, probably your compare favourably to most MSci programmes as well. I would not worry much in that aspect. Having strong grades in those six years will be more important than what one equates your certificate to. (Assuming your references, cover letter, etc. are the same.)
This really depends on the college and the department you want to get into. You should look around for some candidate programs and see what you can find online, and talk to some of the professors who work in that department.
At my university, the postgrad program directors wanted to see work experience. They wanted to see that you'd gone out into the world, and put your learning to the test beyond the confines of an internship. The more real experience you have, the more benefit you'll extract from the program - and the fewer questions you'll have to ask in class. However, this doesn't mean ALL postgrad departments are like this. Perhaps in your field they expect to see someone go straight from undergrad to graduate without working in the field for a few years. Perhaps some departments will care about this, and others won't. It depends on where you go.
It's a good idea to establish some contacts with the advisors now, so that they can come to recognize your name and help you out a little. You might just find an e-mail one day that one of them sends you about an important change, which wasn't sent to others, because they didn't bother to maintain contact. Social networking is very important!!!