For this, you need to consider 5 things:
1. Doppler Effect
2. Multipath (in narrow enclosed environment with high reflective structures or undulated surfaces)
3. Atmospheric absorption
4. Micro/Macrocell size
5. MSC and B-Node Switching response
If you know all the above, you can determine the latency.
Once you know the latency, you can then address your moving speed.
Moving speed within a cell is almost instantaneous.
Moving speed from cell to cell, or service space of a telco operator to a different service space of another telco operator is subjective.