I have a Reliance Netconnect Huawei EC1262 modem and an MTS Mblaze ZTE AC2766 modem.
I was successful in getting the Huawei modem connected on a native install of Ubuntu 10.04 earlier, through the Gnome Network Manager interface. However, after I switched laptops, I have been using Ubuntu from a USB pendrive with persistence, and the Huawei modem did not get connected. Later, I was able to connect with wvdial, but I don't have much experience to share about its quality or reliability.
I tried using both modems on my desktop with Mandriva Free 2010, but somehow trying the ZTE modem's inbuilt package and UI hosed up my X server, and (thanks to a bad 2010 Spring DVD from Linux4u), I had to eventually install OpenSuse 11.3 (Fedora 13 did not boot properly on my old system).
I tried using both the modems on Gnome under OpenSuse, but only the ZTE one works, without even having to install their UI or onboard package, through Network Manager. The Huawei EC1262 still does not work, although it does get recognized as a CDMA modem. I have been unable to use it with wvdial as well, because it or wvdialconf are unable to recognize it. I think the oft-quoted issue of the modem showing up with different IDs between uses is also experienced by me.
I don't have many nice things to say about the connection quality with MTS Mblaze, either on my desktop or my laptop. The Reliance connection has worked better for me.