Problems with streaming music iOS AVPlayer

I'm having some weird issues with AVPlayer. I have a very simple music player (which plays music samples from the iTunes store), working correctly on the simulator (iPhone and iPad with iOS 5.1), but it behaves abnormally on a real device.

On iPad 2 with iOS 5.1.1, it plays correctly even if I connect my headphones to the device. But as soon as I turn them off, it will not play sound through the speakers (although if I plug them in again, I can listen to the song).

On an iPhone 4 with iOS 5.1 installed, it doesn't seem to play through the speakers at all, but I can listen to music through the headphones. Despite the fact that it does not reproduce the speakers, I can hear how fast the music plays (and can confirm that it actually plays, because my user interface responds accordingly), although this seems random.

I use AVPlayeras it seems to fit the bill. Should I use a different library? Do I need to manually direct the sound? Why am I having such problems? And am I using Audio Sessions correctly?

Media.h:

#import <Foundation/Foundation.h>
#import <AVFoundation/AVFoundation.h>
#import <AudioToolbox/AudioToolbox.h>

#define NOT_PLAYING -1

@protocol MediaDelegate <NSObject>
@optional
- (void) didEndPlayingAtIndex:(int) index;
- (void) startedToPlayAtIndex:(int) index;
- (void) stoppedToPlayAtIndex:(int) index;
- (void) startedToPlayAtIndex:(int) to fromIndex:(int) from;
- (void) pausedAtIndex:(int) index;
@end

@interface Media : NSObject <AVAudioSessionDelegate>

@property (nonatomic, assign) int currentItem;
@property (nonatomic, strong) NSURL *url;
@property (nonatomic, strong) AVPlayer *player;
@property (nonatomic, assign) id<MediaDelegate> delegate;

- (void) toggle:(int) index;
- (void) stop;

@end

Media.m:

#import "Media.h"

@implementation Media

@synthesize currentItem;
@synthesize player;
@synthesize delegate;
@synthesize url;

- (id)init
{
    self = [super init];
    if (self) {
        NSError *activationError = nil;
        NSError *setCategoryError = nil;
        AVAudioSession *session = [AVAudioSession sharedInstance];
        session.delegate = self;
        [session setActive:YES error:&activationError];
        [session setCategory:AVAudioSessionCategoryPlayback error:&setCategoryError];

        if(activationError || setCategoryError)
            NSLog(@"ERROR: %@, %@",activationError,setCategoryError);

        self.currentItem = NOT_PLAYING;
    }
    return self;
}

- (void)dealloc{
    NSError *activationError = nil;
    [[AVAudioSession sharedInstance] setActive:NO error:&activationError];

    if(activationError)
        NSLog(@"ERROR: %@",activationError);

    [self.player removeObserver:self forKeyPath:@"status"];
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{    
    switch (player.status) {
        case AVPlayerItemStatusReadyToPlay:
            [self.player play];
            if([self.delegate respondsToSelector:@selector(startedToPlayAtIndex:)])
                [self.delegate startedToPlayAtIndex:self.currentItem];
            break;
        default:
            break;
    }
}

- (void) toggle:(int) index{
    if (self.currentItem == NOT_PLAYING) {
        self.player = [AVPlayer playerWithPlayerItem:[AVPlayerItem playerItemWithURL:self.url]];
        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(didEnd:)
                                                     name:AVPlayerItemDidPlayToEndTimeNotification 
                                                   object:self.player];
        self.currentItem = index;
        [self.player addObserver:self forKeyPath:@"status" options:0 context:nil];
    }
    else {
        if (self.currentItem == index) {
            [self.player pause];
            if([self.delegate respondsToSelector:@selector(stoppedToPlayAtIndex:)])
                [self.delegate stoppedToPlayAtIndex:index];
            self.currentItem = NOT_PLAYING;
            [self.player removeObserver:self forKeyPath:@"status"];
            self.player = nil;
            [[NSNotificationCenter defaultCenter] removeObserver:self];
        }
        else{
            [self.player replaceCurrentItemWithPlayerItem:[AVPlayerItem playerItemWithURL:self.url]];
            if([self.delegate respondsToSelector:@selector(startedToPlayAtIndex:fromIndex:)])
                [self.delegate startedToPlayAtIndex:index fromIndex:self.currentItem];
            self.currentItem = index;
        }
    }
}

- (void) stop{
    [self.player pause];
    if([self.delegate respondsToSelector:@selector(stoppedToPlayAtIndex:)])
        [self.delegate stoppedToPlayAtIndex:self.currentItem];
}

-(void) didEnd:(id)sender{
    if([self.delegate respondsToSelector:@selector(didEndPlayingAtIndex:)])
        [self.delegate didEndPlayingAtIndex:self.currentItem];
    self.currentItem = NOT_PLAYING;
    [self.player removeObserver:self forKeyPath:@"status"];
    self.player = nil;
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}

#pragma mark - AVAudioSession delegate

-(void)beginInterruption{
    NSLog(@"Interruption");
    if(self.currentItem != NOT_PLAYING){
        [self.player pause];
        if([self.delegate respondsToSelector:@selector(pausedAtIndex:)])
            [self.delegate pausedAtIndex:self.currentItem];
    }
}

-(void)endInterruption{
    NSLog(@"Ended interruption");
    if(self.currentItem != NOT_PLAYING){
        [self.player play];
        if([self.delegate respondsToSelector:@selector(startedToPlayAtIndex:)])
            [self.delegate startedToPlayAtIndex:self.currentItem];
    }
}

@end