Have you checked your phone settings to see if by any chance the settings have gone from GSM/WCDMA to GSM only? What phone are you using?
They are different communications channels/subsystems.
And the channel rather than the CPU/SoC data processing will always be the bottleneck.
As such I disagree that the wifi speed is in any way relevant to the query here about carrier data throughput/rates.
But I'll leave it at that as the theoretical discussion is not really answering the question posed.