For loading custom objects in an array, this is what I've used to grab the array:

NSUserDefaults *currentDefaults = [NSUserDefaults standardUserDefaults];
NSData *dataRepresentingSavedArray = [currentDefaults objectForKey:@"savedArray"];
if (dataRepresentingSavedArray != nil)
    NSArray *oldSavedArray = [NSKeyedUnarchiver unarchiveObjectWithData:dataRepresentingSavedArray];
    if (oldSavedArray != nil)
        objectArray = [[NSMutableArray alloc] initWithArray:oldSavedArray];
        objectArray = [[NSMutableArray alloc] init];

You should check that the data returned from the user defaults is not nil, because I believe unarchiving from nil causes a crash.

Archiving is simple, using the following code:

[[NSUserDefaults standardUserDefaults] setObject:[NSKeyedArchiver archivedDataWithRootObject:objectArray] forKey:@"savedArray"];

As f3lix pointed out, you need to make your custom object comply to the NSCoding protocol. Adding methods like the following should do the trick:

- (void)encodeWithCoder:(NSCoder *)coder;
    [coder encodeObject:label forKey:@"label"];
    [coder encodeInteger:numberID forKey:@"numberID"];

- (id)initWithCoder:(NSCoder *)coder;
    self = [super init];
    if (self != nil)
        label = [[coder decodeObjectForKey:@"label"] retain];
        numberID = [[coder decodeIntegerForKey:@"numberID"] retain];
    return self;