Huawei E3131 & E3231 3/4G dongles with RB751

Has anybody had any success with these 3G dongles?

They are HiLink dongles so need the modem switch which I have done and I can use terminal to talk to the modem, send AT commands etc.

But cannot get the thing to connect and get a WAN IP address, despite trawling the forums for ideas from other huawei models - tried a lot of stuff.

Any ideas would be greatly appreciated as these seem to be the latest offerings from the mobile networks.