It is fairly simple to insert a SIM card inside the MX2 modem. Here's a detailed walkthrough of how you can do that:
Open the MX2 modem by sliding the back panel while applying pressure.
As in the below picture, apply down pressure on the metal plate that holds the SIM card in place and slide it open along the direction shown in Figure 1 in the picture.
Insert the SIM card as shown in Figure 2 in the picture and make sure that the SIM card is oriented correctly to match the shown in Figure 2.
Hold the SIM in place by sliding the metal plate reversely on it, as shown in Figure 3 in the picture.
Note: We are currently in the process of creating a YouTube video that will provide a comprehensive guide on how to insert SIM cards into MX2 modems.