Is it mandate to claim itc on a purchased item wrt expense?

we are Govt. Civil-Engg. Works Contractor, (this is the first time we enrolled ourselves with GST/VAT etc.. we were unregistered-before for past many years) 
our partnership-firm has brought a computer today, as-well-as we have some post-paid mobile phones from past few years (which are used for day-to-day office work) , 
Now, is it necessary that, we have to claim ITC on the purchased computer today & monthly mobile bills we recieve every month ? to show them as an expence for our partnership-firm? 
or; 
we can show them as our partnership-firm's expence without claiming ITC like we used to do before enrolling into GST ?