I hope your friend has unlimited mobile data with no monthly cap...
This was mainly what I'm concerned with. This won't be my main internet connection, I have wired connections at home and the office. But I travel around 12 days a month, and won't always have access to wi-fi. I have loooong periods of intense boredom (waiting basically) when FFXIV would be fantastic to be able to boot up and play a bit.
I just want an acceptable connection (doesn't have to be lightning fast, lets face it FFXIV isn't exactly intense gaming - I can play with one finger half the time), and wanted to be assured that 3GB/5GB is going to be enough so I don't vastly exceed the limit and have large bills.
I play the game on a tethered connection about 8 days each month. If you buy a Droid phone, you can get an App which is free, called PDAnet. http://www.junefabrics.com/android/
I actually bought it (16 bucks it unlocks HTTPS, Secured connections), because it is a great deal. The downside is you have to have your phone plugged in all the time, but its self charging and with a Wifi tether you would need to to be plugged in anyway to something cause it will drain your battery fast.
If you only surf the web and NO video then you will be fine, and never reach a 5 GB cap. If you do light youtube at 360p you will be fine also. I use about a 1-2GB of light surfing at leaving the game on for about 64 hours, I afk a lot.
On this it all depends on, where your at and what tower your connected too. Some towers are just laggy and over populated, while some are perfect and you will get 1.3 mbps consistent. Ping on a good tower is 100-250ms which is perfect for any gaming. A bad tower will cause intermittent d.c you might lag out of the game, or get a lot of R0. This can depend on Weather, or happen randomly. Some times on a good tower, I will just d.c all night and either put up with it or just not play. Also if you use a the PDAnet, Incoming Text message will interrupt the data connection. This is because of Verizon's CDMA technology doesn't allow for both the Phone/text and data connections to work at the same time. I am not sure if this happens with the official solution because I heard it doesn't but I would assume it does, so if you do a lot of text while on the connection be wary, while most of the times you won't d.c you will R0 for a short time.
My advice would, get your Droid phone, don't get the Wifi tether just yet, cause it cost extra money. Check out PDAnet, and test it out that way. If you want a more official solution and it works out good, upgrade to the wifi tether support.(OR you can Root your phone and get it for free)