I am using OLS model to predict overall price of fixed phone montly subscription in order to estimate price index. Explanatory variables are only the one user looks after when signing phone contract like free minutes, megabytes etc. Among these variables I've included level of call price as something that user buys as any other features that form a bundle = phone plan.
It was argued that call price is causing endogeneity.
Mine explanation is that the possible bias in the coefficients should not be exaggerated; they're are not as important in estimating overall price of phone plan to calculate price index as in estimating e.g. price elasticity of demand.
What could be a reasonable explanation to rebut this claim about endogeneity? Any other ideas?