To my knowledge, EMI from on board electronic devices has been found to be *detectable* in aircraft electronics, but has never been found to be the cause of an unexpected event or anomaly.
A reasonably thorough investigation of possible EMI was conducted for Quantas 72, which experienced uncommanded pitch downs. Proximity to a naval base with a high power transmitter was investigated as well as an assortment of on board devices. The detailed results, I can't find (probably in an appendix somewhere), but the accident report summarizes the results on pages 3-4. There was no finding of any anomaly resulting from EMI.
airsafe.com/plane-crash/atsb-qantas-a330-interim-report2.pdf
Over the years, cell phones radiation has been generally reduced and bands have changed with each new "generation."