Hi Babers,
It is absolutely not essential to own a cellphone in this business.
It is advisable to call new prospects and leads by phone. This will definitely increase your conversion rate. However, you can of course call from any phone you choose. It does not need to be a cell phone.
And calling leads or prospects is not essential, simply advisable. You can email them if you like, or even use postal mail. And keep in mind GDI also sends out several emails on your behalf when someone shows interest in GDI.
Hope this helps answer your question.
Vincent Parker