This paper presents a study of antennas and package options for mm-scale Internet-of-Things (IoT) applications. Specifically, silicon interposer and organic package substrates with areas ranging from 2.1$\times$2.1~mm$^2$ to 6$\times$5~mm$^2$ are explored. The antennas are electrically-small loop and dipole antennas operating at 900~MHz and 5.8~GHz in the sub-6~GHz bands; and dipole antennas operating in the 28~GHz mm-wave band. The antennas are designed in the context of small sub-mm integrated circuits. We find that both silicon interposer and organic package substrates can achieve similar antenna performances across frequencies even though they have different constraints. Our system analysis shows that for a given EIRP limit, 28~GHz achieves the highest range for smaller 2.1$\times$2.1~mm$^2$ substrates.