The use of the CCS purchasing platform for mobile phones within the public sector

Dear All, I would like to know 3 things: - a.) is it mandatory to use the CCS purchasing platform to purchase mobile phones? b.) if you do use it - have the delivery response times been good? c.) if you do not use it, what option do you use to conform to the public sector procurement regulations in terms of aggregated spend in relation to purchasing mobile phones for your company? Thank you