A very simple question(Zigbee)

I am new in Zigbee.
'ZigBee operates in the industrial, scientific and medical (ISM) radio bands; 868 MHz in Europe, 915 MHz in countries such as USA and Australia, and 2.4 GHz in most jurisdictions worldwide.'

I get confused about this statement.
My question is , Are both of 868MHz and 2.4GHz used as ISM band in the UK?

yes

what is exact mobile phones range(GSM band) at 900 MHZ?Is there any overlap between 915(902-928MHZ) ISM band and 900MHZ GSM band?

http://en.wikipedia.org/wiki/GSM_frequency_bands
there is overlaping