The BSNL EVDO service is being billed under Landline CTBS system in most parts of India. Since this system is in practice from long time, most customers are used to it. But Chennai customers need to undergo a small change in their billing system.
Recently in Chennai, BSNL has changed their billing system from Landline CTBS to GSM billing system. Which means if you pay your current/next bill under regular landline CTBS counter, your subscription won’t be updated and will be manually transferred to GSM billing system. And so there will be a delay during the period of transition. So tha might end up in disconnection of internet unless you contact some customer service executive and get it fixed.
So to over come this issue, vaithy (our forum member, who reported this) has a suggest for all Chennai customers. To read the suggest to overcome this issue, head over to this thread.