This post is great: it shows you how to silence your iphone, except from a selected number of contacts.

to set this up on your iphone,

with ios7:

settings > do not disturb >

in ios7 you have options for ‘manual’ and ‘scheduled’

manual means that you can turn this feature on and off yourself, and scheduled means that your phone will automatically enable do not disturb on its own

in ios6 go to

settings > notifications > do not disturb

in ios6 you dont have the manual option, only the scheduled one.
to enable do not disturb in ios6 go to
settings > toggle the ‘do not disturb’ option.

in both ios 6 and ios7 in the do not disturb options you have three optioins for the ‘allow calls from’ option:

if you pick ‘favourites’ then your iphone will only ring when people you have marked as favourites call.

if you pick from the ‘groups’ then your iphone will only ring when contacts added to those groups call.