Mine started sleeping through - like 8pm to 6am (on a regular basis) at about 10 months. Some people claim theirs slept through from 3-4 weeks old; when they actually mean 11.30pm til 4.30am. An actual regular proper night's sleep won't usually start til they are 9-12 months old; like 10 hours I mean.
It's a fairly well documented fact that formula fed babies start sleeping though the night earlier, as with a full bottle of formula (7 to 8 oz) a baby will have a full tummy for 7-8 hours, but a breastfed one will need another helping after 3-4 hours.
It's still better to breastfeed if you can though, if only for 4-5 months. I would never switch to formula when I was able to breastfeed, just for the sake of being able to sleep through the night sooner.
Even when they start sleeping through for 8-10 hours, you will get 4 to 7 nights a month where they will wake because they wet or pooed themselves, or are hungry, or they have had a bad dream. With mine, this went on til they were about 2 to 2 and a half y.o. They still woke occasionally through the night when they were 3 to 4 y.o. but it was only like once or twice a month. Then past 4, they pretty much always slept though from 8pm to 7am.
The first time I got a decent lie in (on a regular basis,) was when they were 3 and a half to 4 y.o.