This study examines the causal impact of 3G mobile network coverage on fertility decisions in Nigeria using geo-referenced data from the Nigerian Demographic and Health Surveys (2013-2018) combined with mobile coverage information. Employing two-way fixed effects for fertility analysis, the analysis reveals that increased 3G coverage significantly reduces birth rates among adolescent women aged 12-20. The spatial gradient of effects—stronger within 30km of network coverage and diminishing beyond 40km—provides evidence of a causal relationship. The primary mechanisms driving these effects include delays in age at first marriage, postponement of first childbirth, and increased adoption of modern contraception methods. These findings suggest that investments in telecommunications infrastructure may yield substantial demographic benefits through reduced fertility rates, particularly among adolescent women. 2025 AAEA & WAEA Joint Annual Meeting, July 27 - 29, 2025, Denver, Colorado