Flow control method for reducing the congestion in the Abis interface in a mobile telecommunication system, in which every established data call has two associated parameters: a 'downgradeable' flag (also for the voice calls) to consider if the data call can be downgraded or not, and the minimum Abis bandwidth for the data call, BW MIN . The flow control is activated whenever the Abis occupancy exceeds a flow control activation threshold (FCAT), is deactivated (S0) whenever the Abis occupancy goes below a flow control deactivation threshold (FCDT), and comprises: analyzing (S2) established data calls one by one; in case a data call can be downgraded and is using Abis resources over its BW MIN (S3), downgrading (S4) said data call to its BW MIN ; analysing (S7) established voice calls one by one; in case a voice call can be downgraded and is a full-rate call, and also the corresponding mobile terminal is half-rate capable (S8), downgrading (S9) said voice call to half-rate.