aruran,

I'm sorry, but I really can't tell which cable to use with the 7250i.

For my tests I used a 6210 with a standard (NoName) Data cable.

All I can tell is:
If your Phone doesn't respond to AT-commands sent from Hyperterm there is most likely something wrong with your cable.
I had two different cables, one did work, the second one didn't. I haven't taken the time to investigate in detail what the difference between them was.

To find out which cable works with your particular phone (or how to build your own) I guess you will have a better chance on one of the many GSM-Forums.