Couple of bits of advice needed please. First I cannot figure how to call a contact using sipgate instead of the mobile network, if I go to dialpad I can choose call type but it is unclear to me how I choose sipgate instead of cellular for an existing contact.

Secondly I am trying to call home on sipgate by dialing the same voip number logged on my phone. I can be heard but I cannot hear home on my 900. Any ideas please?

Look at the contact card. You should see a button to call using SIP. My phone isn't at hand at the moment, so I can't quote exactly what it says.

Have you checked

Use for telephone numbers

in the advanced SIP settings?

Are you behind a NAT router?

I dont use sipgate but I do use other types of services. Basically, when you open a contact card, you can see the option to call by using sip. Another way is when you open the dialpad, you can tap on
Phone -> Accounts-> and choose the account you wish to use (e. g. sipgate)

Thank you, problem solved - I was looking without being 'available', as soon as I made myself available the option to dial using SIP Audio was shown in the contact card so this is my fault.

I am behind a NAT router, it's a Linksys, any idea what I may need to tweak if this is the problem? The router is dedicated VOIP though, not through the router, so it is all in one unit.