For me maintained implies continuation of service for the required term (15 days). Other than that, there is no metric dictating a certain amount of usage on that phone/service. I got the cheapest plan and opened up the box to turn on the phone, made one call and switched the phone off to never turn it back on until I cancelled the service. But, before I cancelled the service, I chatted with a Citi rep and he said I completed the requirements for the credit and should get it in 2-3 statement cycles. Though their assurances are not 100%, I believe buying the phone and having the service for 15 days is good enough for the credit.