Hm, why don't you take a photo and ask on a font forum? Maybe they can help. The resolution is a bit low, so it's hard to tell. Unfortunately I've just changed the font on my M6, so I can't really tell, but judging from
http://img148.imageshack.us/img148/249/338297lv8.jpg it isn't Arial (look at the R), and Tahoma can be excluded too. It's a font that is very close to Helvetica, however the G hints towards Univers. The R also hints more towards Univers, but it seems to be even more angled than Univers. The a also looks a bit different, but I think Univers should a very close match, differences may be because of a different version or the low resolution.