Two lines into ONE phone

[The King]

Hi guys,

I have a Grandstream 496, which has two seperate rj11 ports, which I can configure to two seperate SIP providers.

What I want to do is use BOTH these lines on one phone (one SIP provider for incoming, another for outgoing).

I tried to use a basic line splitter in reverse, but that way when I dial out it tries dialing on both lines!!

What I need is one of these;
ATT 2-LINE SWITCH Now you can easily join your two single line telephones in 1 switch

BUT - I am in the UK, and can't seem to find this anywhere! Anyone know what this is called? I've tried ebay and Maplin, but can't find it anywhere, not sure what it is called (2 line switch doesn't bring any results!)