Currently, all mTrak units take a mini SIM, which is 25 x 15 mm and is the largest SIM in common use.

Wikipedia, as ever, explains the sizes.

If you supply your own SIM card, before fitting it to the mTrak unit, there are a several things that you may need to do, or that would be more convenient to do while you have the SIM available.

You may need a mobile phone that can be used with the SIM that you are using.

You need to:-

• Make sure that the SIM can send and receive texts and can receive calls.
• Make sure that the SIM can access the internet.
• Find the phone number of the SIM
• On a Pay As You Go SIM, make sure that you can find the credit once the SIM is fitted to the mTrak unit.
• On a Pay As You Go SIM, make sure that you can top up the credit.

On some networks, the SIM can be topped up by getting it to use a code that includes a voucher number.

It may be possible to top up at a cashpoint machine.

Finding the balance and topping up can be done at the websites of most PAYG providers. The SIM needs to be registered on the network's website for that, and registering usually has to be done before the SIM is put in the mTrak unit. The procedure depends on which network the SIM is on, so it is best to look at the network's website.