Possible way to detect sim card detection in ios?

You can check it by CTCarrier class.

BOOL isSimCardAvailable = YES;

CTTelephonyNetworkInfo* info = [[CTTelephonyNetworkInfo alloc] init];
CTCarrier* carrier = info.subscriberCellularProvider;

if(carrier.mobileNetworkCode == nil || [carrier.mobileNetworkCode isEqualToString:@""])
{
    isSimCardAvailable = NO;
}

You need to add CoreTelephony framework for using CTTelephonyNetworkInfo and CTCarrier.

By the below code you can get the sim card details like carriername,mobilecountrycode,isocountrycode,mobilenetworkcode.In the ios 6 all are retained.So if your sim card is removed also it will retain the old details.So there this idea wont be useful but in ios 7 only carriername is retained and remaining are changed so the below code can be used

CTTelephonyNetworkInfo* info = [[CTTelephonyNetworkInfo alloc] init];
CTCarrier* carrier = info.subscriberCellularProvider;
NSString *mobileCountryCode = carrier.mobileCountryCode;
NSString *carrierName = carrier.carrierName;
NSString *isoCountryCode = carrier.isoCountryCode;
NSString *mobileNetworkCode = carrier.mobileNetworkCode

// Try this to track CTCarrier changes 
info.subscriberCellularProviderDidUpdateNotifier = ^(CTCarrier* inCTCarrier) {
        dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"User did change SIM");
        });
};

Implemented in Swift as a read-only computed property:

import CoreTelephony

var availableSIM: Bool {
    return CTTelephonyNetworkInfo().subscriberCellularProvider?.mobileNetworkCode != nil
}