if you want to send sms within india, i prefer Way2SMS.
if you are using a pc to send sms, link is *way2sms.com/
and if you are using a mobile, link is *wap.way2sms.com/
delivers in seconds and worked 100% for me except on last friendship day when the sms were delayed, but i guess that was normal for that day.
please note the sms is limited to 110 characters though you can send as many as you want.
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if you want to send international sms, i haven't found a better website than *wadja.com/ this is much like a social networking site but it is meant for sending international sms. i don't the have the wap link though.