I have used a cellular card for years with both PC and Mac laptops. Most recently I was using an expresscard34 card with my MBP. Since I needed to change to a USB card, I thought it would be good to do a comparison between AT&T and Verizon. I purchased a Verizon UM150 and an AT&T USBConnect 881. Both fit the MBA. For those of you that do a lot of traveling, having a cellular modem you can plug into your laptop can be a liberating experience. The cards are pretty cheap ($50-$100 after rebates and 2 yr contract) and the monthly connection fee is $60. Again, if you do a lot of traveling you would incur over $60 of connection charges pretty easily. Both are the same size (not small) and both have a pop out usb connector. The Verizon card has the advantage of containing a MicroSD slot (for which I ordered a 12GB card), so you only need one USB slot (which is good since I only have one). The Verizon card also has an antenna which can be extended. The AT&T (SierraWireless) card has the advantage of being GSM based (contains a SIM card) which means it can be used overseas on any GSM network (watch out for roaming charges). Now for the speed tests. I did some testing over a couple of days with both. I had to replace the AT&T card when it died on me. They were very nice and did the exchange with no hassles. I noticed very little or no difference with regards to signal availability or connection speeds. I used dslreports.com to do some back to back speed tests. I did five tests on each unit twice (ten total). One group in the morning and one in the afternoon. download average (kbps) upload average (kbps) latency (ms) Verizon 1,010 505 117 Cingular 903 652 165 As you can see, Verizon is slightly faster on the downloads and slower on the uploads. Verizon also has less latency. One thing I did notice is that Cingular, while slightly slower, was more consistent in the download speed. Bottom line is that unless you plan on doing a lot of uploading (which I wouldn't), then its a wash as to which service you use. If you already have Verizon, stick with that service (the same goes for AT&T). I have both services at the office, so I'm going to stick with the Verizon card, because it has the MicroSD slot.