In 3GPP, a narrowband system based on Long Term Evolution (LTE) has been introduced to support the Internet of Things. This system, named Narrowband Internet of Things (NB-IoT), provides low-cost devices, high coverage (20 dB improvement over LTE/GPRS), long device battery life (more than 10 years), and massive capacity. Latency is relaxed although a delay budget of 10 seconds is the target for exception reports. NB-IoT can be deployed in three different operation modes - (1) stand-alone as a dedicated carrier, (2) in-band within the occupied bandwidth of a wideband LTE carrier, and (3) within the guard-band of an existing LTE carrier. In this paper, we undertake a deployment study of NB-IoT using existing LTE infrastructure. We consider the case when only a fraction of the existing LTE cell sites support NB-IoT (so called partial deployment of NB-IoT). In this case, NB-IoT devices cannot attach to the best cell if that cell does not support NB-IoT. As a result, the path loss can be very high. In addition, they also suffer from high interference from non-NB-IoT cells. We examine potential techniques to compensate for the high path-loss and high interference and provide analysis to indicate when partial deployment of NB-IoT is feasible. We also examine interference issues in asynchronous deployments and study performance.