I'm just curious, if I block another Boost Mobile phone number from texting or calling are they notified?
Boost does not have an account level selective block for voice calls. Instead, you can do it from your Android or iPhone.
Android: Blocking from Android applies to calls and texts. Calls ring once and go to Voicemail, texts are sent to a "blocked senders" folder. As you can see, it's more of a re-routing than it is actually blocking, but no notification is sent to your ex BFF, they're just shuffled off to a place you don't have to see if you don't want.
To Block a number in Android from their contact window, click the three button menu at the top right corner of the screen and select "Block number." Callers will hear a half ring and then go straight to voicemail. You can decide if you want to listen to the VM or not.
You can get to the Contact window by clicking the person's name or number directly in your call log or by clicking the three button menu at the top corner of their message screen, go to People and Options then click their name again.
If you block someone from texting you from your Boost account settings, they get a message that you have chosen not to receive messages. Though it doesn't say 'chosen not to receive messages FROM YOU,' your ex BFF will probably know you blocked them. Still worth it if you're being harassed or abused.
We've been talking about Android phones but for iPhone users who may be reading, be aware that selective text blocks will not block iMessages. You'll need to do that from iTunes (instructions for that here).