Is it permissible to use a cell phone during I'tikaaf?

Answer

Whilst it is permissible to use the cell phone during I'tikaaf for necessities as explained by you, it is in conflict with the spirit and purpose of I'tikaaf. I'tikaaf is a period of renunciation from the outside world. As far as possible one should abstain from outside contact and engage in only ibaadat – Muraaqabah (contemplation), Thikr, Salaat, Tilaawat, Istighfaar, etc. If tired, sleep, but don't engage in conversation with others who are sitting in I'tikaaf. Only if there is a dire need, should the cell phone be used.

I'tikaaf is an ibaadat in which there should be peace, solitude and seclusion. Nothing should be done to disrupt the spirit of the I'tikaaf. Therefore, abstain as much as possible from using the cellphone. If you have to use it, use it as little as possible and keep the talk as brief and as formal as possible.