With iOS7, Apple have introduced a function to block phone numbers from calling or texting you and also to block Facetimes. You don't need to jailbreak your phone either as the function is part of iOS7! :)
Phone numbers already in your contacts list can be added to the block lists here:
Settings > Phone > Blocked > Add New
Settings > Messages > Blocked > Add New
Settings > Facetime > Blocked > Add New
Blocking a number which has recently called you (eg a telemarketeer) can be done through the call log
click the "i" next to the number in the call log > scroll down to "Block this Caller"
Simples!
http://ios.wonderhowto.com/how-to/block-any-unwanted-callers-phone-number-your-iphone-ios-7-even-if-theyre-not-your-contacts-0147388/