This pronunciation phenomenon appears to be more widespread than I'd thought. I've always pronounced lawyer as it's spelled (law-yer), but I've often heard people say loy-er instead. It's not dialectical as far as I can tell, since so many different people say it that way (plus, it's in the dictionary). Why is lawyer so often pronounced loyer?
The OED has both /ˈlɔːjə(r)/ and /ˈlɔɪə(r)/. In my British accent, I tend towards the second. The reason it’s so widespread, if indeed it is, may be because the transition to the vowel /ə/ (schwa) is more readily made from the diphthong /ɔɪ/ than it is from the sequence of /ɔː/, /j/, but I readily yield on the point to any phoneticians among us.