We have problems with our broadband supply from BT so we upgraded the router to a 2860Ln with 4G and inserted a Vodafone data only SIM which worked very well for internet access but when it failed over to 4G our BT cloud Voice phones do not work? Has anyone successfully set this up or can anyone offer a solution to this issue.

Is this a NAT issue at the telco... what type of IP address does the 4G WAN get (private range or routed) - you might need to use STUN/NAT-T on the phones...

Thank you for your response, unfortunately I am not at the site where the issue is today and can not test this again but when I was testing this on Friday we were getting a different IP than our static ip allocated by BT but without actually doing the test again I don't know. I can tell you that other than getting the fibre broadband online and the 4G Vodafone data online I have not done anything else to the router with regards to NAT We spoke to the premium support line and they mentioned the same things but I have barely any knowledge of what NAT STUN and NAT-t are so any help you can give me would be really appreciated. Apart from are the ippaddresses 'private range or routed' is there any other info you might need to help us out?

I have remote access to the router so can get any settings you might need to see but local access will have to be tomorrow when surgery finishes at the practice

I was thinking that the 4G provider might be adding their own NAT, not the router (which will add it too). If the ISP applies CGN (NAT) then you don't have a publically routable address. NAT-T and STUN - raise a support ticket or see if there are any knowledgebase articles.