The present study examines the effect of two potential catalysts for interlanguage phonetic interaction, code-switching and language mode, on the production of voice onset time (VOT) to better understand the role of (near) simultaneous dual language activation on phonetic production, as well as the nature of phonetic transfer. An oral production paradigm was carried out in which Spanish–English bilinguals produced words with initial voiceless stops as non-switched tokens, code-switched tokens in an otherwise monolingual context, and code-switched tokens in a bilingual context. Results demonstrated a degree of phonetic transfer associated with code-switching, either unidirectional or bi-directional. Specifically, English, with long lag VOT, was more susceptible to phonetic transfer than Spanish (short lag). Contrary to expectations, while the code-switching effect was present in both monolingual and bilingual mode, there was no additional transfer, or additive effect, of bilingual language mode. Differences in the effects of code-switching on English and Spanish are discussed with respect to the inherently different acceptable VOT ranges in the two languages. Furthermore, the lack of difference in VOT between the code-switched tokens in the monolingual and bilingual contexts is taken to suggest limits on phonetic transfer.