If you need to call someone and you don't have a SIM card, there are a few methods you can use. One is to use a VoIP (Voice over Internet Protocol) service like Skype or Viber. These services allow you to make calls using an internet connection instead of a cellular network. Another option is to use a temporary or emergency phone number service. These services provide you with a temporary phone number that you can use to make and receive calls. The downside of this method is that the number is only good for a limited time and it may not work in all countries. Finally, if you have access to another person's phone, you can borrow their SIM card and use it in your own phone to make the call.