FW500 - Emergency Back UP Telephone

[JoRo1948]

I have just become the proud owner of a FW500 telephone.  This phone works as a conventional digital-landline phone, but if there is a power cut it automatically switches over to being a 4G mobile phone. .

The leaflet which accompanied the phone states it has a SIM card already inserted which is loaded with "a limited number of minutes" and should be used only in an emergency.  Does anyone know how many minutes are available with this SIM?

Is it possible to replace the SIM supplied by EE with another of my choosing, not necessarily a different network, just one with lots of minutes that I could use as and when I wish.

Finally, a very trivial matter but I like to know these things.  Can anyone tell me where the microphone is situated for the hands-free operation?  Is it the hole near the SIM card slot?

As always, I am grateful for any and all replies.

[JimM11]

@JoRo1948 Start here and go, see what you can work out.

BT FW500 Hybrid Back Up Phone (117693) | EE Store

Digital Voice Motorola FW500 Hybrid phone | BT Help

[JoRo1948]

Thank you for your response. 
I have looked at both links. Unfortunately neither elaborate on the number of minutes available or whether I could use a different SIM card. However, I was pleased to see that EE will replace the battery in the phone if it fails. There is no mention of any charge being made.