Hi,
I have a huwaei e220 - it works with this. I picked one up for £8 and (unlocked it myself for free).
It has better performance with 1.21 fw - but with this fw, it has issues for me and you have to fiddle with the settings to get it running after a router power cycle - (I have to do this quite often as my normal wireless connections stops working after some days!!)
It works "smooth" with 1.31 fw - I think they fixed a few 3g wan issues (no need to tweak settings) and wireless issues are much less in this fw. But for me, my 3g connection although more "stable" was performance capped at around 50 -70 % . Depending on how fast your 3g connection is anyway, this might be ok for you. This is my own experience but others may be different.
The dlink ones (dwm 15*) - cost more than I paid for this router itself - so defn. not something for me and I can't comment on their performance.
I think the "best" solution is to buy a router with proper / dedicated 3g connectivity support (including your modem) and then connect this to dir-655 for your wireless n needs. This could be cheaper (there are many products that cost less than the dwm 15* modems) and you get "full" 3g performance, however with extra hassle of another box.
Cheerz