There is only one post with the tag 4g and one for lte. Seems most of the questions tagged with 3g was related to mobile data applications - probably it is appropriate to merge these tags into one, say [mobile-data] or [3g/4g/lte].
It may be a bit more of a problem with 3g because there are 145 questions so removing is not an option.
I think the best solution to this problem would be to merge them (like you said).
We will have to wait until a moderator or a high rep user can do this.