If you want the phone to ring for calls but not get notification sounds for text/emails, you can disassociate those volume controls. Go to Settings - Sound settings - Volume and uncheck the box at the bottom. Then you can set separate volumes for the two.
There are apps that allow you to program this to happen automatically at specific times, but I will not recommend one here because when I have tried them in the past, they have caused various problems with whatever phone I was using.
Also, you can always turn off 3G (and WiFi) overnight if you do not need to receive texts and emails during that time (wasn't sure from your post whether you wanted to still receive them but just silently or if turning them off all together would work for you). You can still get phone calls with those off. You can do this right from the notification bar - click on Mobile data (and WiFi if you use that).