Q: I want to send text sms of length 800 character. I know the max limit of sms text is 160 characters.
Is it possible that I will send 5 SMS and each SMS length is 160 (160 * 5) character and user receive only one SMS with the content length 800 character?
A: This is also known as "concatenated messages", see http://en.wikipedia.org/wiki/Concatenated_SMS. Despite it becoming more adopted on handsets, there are still inherent problems, plus adoption rates for these handsets varies by country. txtNation do not currently offer concatenated messaging as we are unable to provide a reliable service for this.
The closest that you can do is to send subsequant gateway / reply=0 messages.
Some clients list them as 1/7, 2/7, 3/7 for example, so the recipient knows which order to read them in.