What are grey or ‘blended’ routes?

Grey or ‘blended’ routes refer to the routes some telecommunications companies use to send bulk SMS. It is a cheap alternative as it exploits the vulnerability of mobile networks but does run the risk of your messages being intercepted, copied (and even altered), delivered much more slowly and in some cases, not delivered at all. 

These routes take advantage of the fact that many mobile networks i.e. O2, to enable their customers to send messages whilst abroad, allow overseas networks to pass messages originating in their countries to the UK, for an agreed fee or, in cases where volume is relatively low, for free. 

In most cases, when you are sending a message between handsets within the UK, you will use the UK mobile network to achieve this. However if you routed this message through a remote country to begin with, i.e. the Soloman Islands and then back to the UK, you could reduce the price of this message to almost nothing. It is this that companies exploit to send their messages cheaper but as mentioned above, it jeopardises the security of the messages and often means a long delay or non-delivery.