By inspecting the user's address book and finding the most common city, state, and zip code - we can make an educated guess as to the user's location without using CoreLocation.

SFBestGuess.h

#import <Foundation/Foundation.h>
#import <AddressBook/AddressBook.h>

@interface SFBestGuess : NSObject {
    NSMutableArray *_cities;
    NSMutableArray *_states;
    NSMutableArray *_zipCodes;
}

@property (nonatomic, retain) NSMutableArray *cities;
@property (nonatomic, retain) NSMutableArray *states;
@property (nonatomic, retain) NSMutableArray *zipCodes;

- (void)guessLocation;
- (void)incrementOrCreateKey:(NSString *)key inDictionary:(NSMutableDictionary *)dict;
- (NSMutableArray *)sortedDescendingArrayFromDictionary:(NSDictionary *)dict;

@end

SFBestGuess.m

#import "SFBestGuess.h"

@implementation SFBestGuess

@synthesize cities = _cities;
@synthesize states = _states;
@synthesize zipCodes = _zipCodes;

- (void)dealloc {
    [_cities release], _cities = nil;
    [_states release], _states = nil;
    [_zipCodes release], _zipCodes = nil;
    [super dealloc];
}

- (id)init {
    self = [super init];

    _cities = [[NSMutableArray alloc] init];
    _states = [[NSMutableArray alloc] init];
    _zipCodes = [[NSMutableArray alloc] init];
    
    [self guessLocation];

    return self;
}

- (void)guessLocation {
    NSMutableDictionary *cities = [NSMutableDictionary dictionary];
    NSMutableDictionary *states = [NSMutableDictionary dictionary];
    NSMutableDictionary *zipCodes = [NSMutableDictionary dictionary];

    ABAddressBookRef addressBook = ABAddressBookCreate();
    CFArrayRef allPeople = ABAddressBookCopyArrayOfAllPeople(addressBook);
    CFIndex nPeople = ABAddressBookGetPersonCount(addressBook);
    
    for(int i = 0; i < nPeople; i++) {
        ABRecordRef ref = CFArrayGetValueAtIndex(allPeople, i);

        ABMultiValueRef multi = ABRecordCopyValue(ref, kABPersonAddressProperty);
        if(multi) {
            NSArray *theArray = [(id)ABMultiValueCopyArrayOfAllValues(multi) autorelease];
            NSDictionary *theDict = [theArray objectAtIndex:0];

            NSString *city = [theDict objectForKey:@"City"];
            [self incrementOrCreateKey:city inDictionary:cities];
            
            NSString *state = [theDict objectForKey:@"State"];
            [self incrementOrCreateKey:state inDictionary:states];

            NSString *zip = [theDict objectForKey:@"ZIP"];
            [self incrementOrCreateKey:zip inDictionary:zipCodes];
            
            CFRelease(multi);
        }
    }

    CFRelease(addressBook);
    CFRelease(allPeople);

    self.cities = [self sortedDescendingArrayFromDictionary:cities];
    self.states = [self sortedDescendingArrayFromDictionary:states];
    self.zipCodes = [self sortedDescendingArrayFromDictionary:zipCodes];
}

- (void)incrementOrCreateKey:(NSString *)key inDictionary:(NSMutableDictionary *)dict {
    if(key) {
        if([dict valueForKey:key]) {
            [dict setValue:[NSNumber numberWithInt:[[dict valueForKey:key] intValue] + 1] forKey:key];
        } else {
            [dict setValue:[NSNumber numberWithInt:1] forKey:key];
        }
    }    
}

- (NSMutableArray *)sortedDescendingArrayFromDictionary:(NSDictionary *)dict {
    NSMutableArray *sortedArray = [NSMutableArray array];
    NSArray *sortedKeys = [dict keysSortedByValueUsingSelector:@selector(compare:)];

    NSString *someKey;
    NSEnumerator *e = [sortedKeys reverseObjectEnumerator];
    while(someKey = [e nextObject]) {
        NSDictionary *tmpDict = [NSDictionary dictionaryWithObjectsAndKeys:someKey, @"key", [dict valueForKey:someKey], @"count", nil];
        [sortedArray addObject:tmpDict];
    }
    
    return sortedArray;
}

@end