Ginota allows you to start receiving concatenated inbound SMS anytime anywhere!
Generally a long SMS is split into chunks of 153 characters while in Unicode content messages are up to 67 characters where extra 8 chars are needed to hold 'segmentation information' that is sent along with the body of the sms, so that the handset knows how to put all the parts back together again into a single long message.
Due to the nature of sms, and networks in general, the different parts may arrive in any order, so this segmentation information is vital for the handset to be able to re-construct the message properly.
One final thing to consider with long sms's, its not always the case that 160 characters will fit into a single sms. There are some characters that in the GSM alphabet that require 2 characters because they are 'extended alphabet' characters. So they need an 'escape' char + a char. A good example is the £ sign or Euro symbol. These 'escape' characters are also taken into account when deciding where to split the message into parts.
Check this wikipedia entry to know more about concatenated SMS