Scrobbl is amazing. It's an last.fm scrobbler that runs as a daemon on your jailbroken iOS device and just checks what you are listening to in Music.app and scrobbles that accordingly. It's probably one of the main reasons why I consider jailbreaking my phone. It's so good!
That is the app's interface. Basically, the app isn't much, you just log in to last.fm there and then you have 4 settings to config: Scrobble Tunes (Music), Scrobble over Edge/3G, Scrobble Podcasts, Toggle Debugging.
This is perfect
I love these settings. They are just what I need. No bullshit.
If you have the Edge/3g Setting off, it will only send now playing notifications on Wifi, and will automatically scrobble the songs you listened to while you weren't on Wifi once you connect to a wifi network, without you having do anything. Perfect.
Now what I find truly amazing over this tweak/daemon is that it was last updated for iOS 5 support. Yet here I am on iOS 8 and it works! On iOS 7 and 6 it worked perfect, on iOS 8 one thing broke, but there is a one-liner to fix that:
mv /System/Library/LaunchDaemons/org.nodomain.scrobbled.plist /Library/LaunchDaemons/org.nodomain.scrobbled.plist && reboot
Basically the location where LaunchDaemons should be stored changed in iOS 8, so all you need to do is move it to the proper location and reload it and it's done!
There is also Scrobbled, which is a fork of this original Scrobbler. Basically, it is an better version: it encrypts the stored password, it uses an new last.fm API to scrobble, it supports other Music apps, and some other stuff. Basically, it's better in every way, and I'm just a conservatist.
If you really wanna jailbreak your phone to scrobble songs, I would probably recommend Scrobbled instead since it's newer, but there is just something about the original Scrobbl I love. It's so simple (Scrobbled has more options) and it's very old and still works (I find that cool). I will probably keep on using Scrobbl until last.fm deprecates the old old scrobbling API that the original Scrobbl is using, then I'll switch to Scrobbled.
Both are these are free anyway, and can be found in Cydia in the BigBoss repo.
So if you ever check my last.fm page and I'm scrobbling from Scrobbl for iPhone, you know what I'm using!