I dont think the internet speeds will suffer, even if there is it'll be marginal. I just got 425kBps max on my torrent and i have a 4mbps conn so thats pretty decent.
The only thing that suffers is the latency or pings which increase by about 20-30ms i guess. google for info. Only important for gaming. For normal web surfing it is too short to be noticed. Although i even game on wifi (PC and PS3) so thats not a prob.
So in short there will be no significant drop in performance. [Unless you live in a mansion

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For some reason the above posts dint show up so im replying now
>NO airtel wont have a problem with it but do ask them what kind of router do you need. They said any router will work when i asked them. I use a WRT-120N @2.5k Its a good one and has served me well and even my friends have got the exact same one (again for a 2mbps airtel conn. shared by 3 people)
I didnt understand by what you mean by the wifi sharing the bandwidth.