Ah yes, the letter ij. Officially it shares its place in the alphabet with the letter y (like in telephone listings), but they're really not the same. Even though it is spelled using both the i and j together, it must be considered a single letter, which becomes apparent when it's capitalised, for example in the name of the largest lake in he Netherlands, the IJsselmeer. As for the pronunciation, I'd say it's somewhat a mix between the English A and I. Note that there also exists the ei, which is pronounced very similar, though there is a subtle difference. The ij is often called the 'long ij' and the ei then is called the 'short ei'. I would say the ei is pronounced a tiny bit 'flatter' than the ij. Ask someone to say the words hij and hei and try to hear the difference. The ei is not a single letter like the ij is, for example in the name of the city Eindhoven, you can see only the e is capitalised. And yes, there are notable differences in the pronunciation in various dialects. Some may sound rounder (more like the English I) and some sound way flatter (like a short e as in 'help').