Detect carrier connection type (3G / EDGE / GPRS)

From iOS 7 on you can use:

CTTelephonyNetworkInfo *telephonyInfo = [CTTelephonyNetworkInfo new];
NSLog(@"Current Radio Access Technology: %@", telephonyInfo.currentRadioAccessTechnology);
[NSNotificationCenter.defaultCenter addObserverForName:CTRadioAccessTechnologyDidChangeNotification 
                                                object:nil 
                                                 queue:nil 
                                            usingBlock:^(NSNotification *note) 
{
    NSLog(@"New Radio Access Technology: %@", telephonyInfo.currentRadioAccessTechnology);
}];

I have also found this to detect a slow or fast connection:

- (BOOL)isFast:(NSString*)radioAccessTechnology {
    if ([radioAccessTechnology isEqualToString:CTRadioAccessTechnologyGPRS]) {
        return NO;
    } else if ([radioAccessTechnology isEqualToString:CTRadioAccessTechnologyEdge]) {
        return NO;
    } else if ([radioAccessTechnology isEqualToString:CTRadioAccessTechnologyWCDMA]) {
        return YES;
    } else if ([radioAccessTechnology isEqualToString:CTRadioAccessTechnologyHSDPA]) {
        return YES;
    } else if ([radioAccessTechnology isEqualToString:CTRadioAccessTechnologyHSUPA]) {
        return YES;
    } else if ([radioAccessTechnology isEqualToString:CTRadioAccessTechnologyCDMA1x]) {
        return NO;
    } else if ([radioAccessTechnology isEqualToString:CTRadioAccessTechnologyCDMAEVDORev0]) {
        return YES;
    } else if ([radioAccessTechnology isEqualToString:CTRadioAccessTechnologyCDMAEVDORevA]) {
        return YES;
    } else if ([radioAccessTechnology isEqualToString:CTRadioAccessTechnologyCDMAEVDORevB]) {
        return YES;
    } else if ([radioAccessTechnology isEqualToString:CTRadioAccessTechnologyeHRPD]) {
        return YES;
    } else if ([radioAccessTechnology isEqualToString:CTRadioAccessTechnologyLTE]) {
        return YES;
    }

    return YES;
}