We present TeamBoost, a collaborative solution enabling a client device to leverage the cellular links of its nearby devices to enhance its overall connectivity to the cloud. TeamBoost architecture can serve for numerous internet-of-things (IoT) applications, yet in this work it is proposed as an alternative to conventional and costly H/W upgrades aiming to maintain up-to-date vehicle connectivity experience throughout the vehicles extended lifetime. TeamBoost's approach is to build upon a relatively new and yet well established Multi-Path TCP (MPTCP) protocol, exploiting the natural way that MPTCP splits an end-to-end single TCP stream into multiple MPTCP sub-streams that traverse different communication links. TeamBoost's novel implementation provides a non-trivial extension of MPTCP to TeamBoost's collaborative setting, where sub-streams are relayed through multiple independent devices. To support scalability of the system, the implementation of TeamBoost on the devices is restricted to the user-space, allowing it to be installed as any other application supported by its operating system (OS). Experimental results show the benefits of TeamBoost, in terms of both connectivity performance and robustness.