It depends on the E70 -- if it's an E70-1 (900/1800/1900) there will be no English-US firmware variant possible, they'll all be English-UK. The E70-2, though, is a real US phone (850/1800/1900) and will have English-US firmware variants available.
Technically (legally?), a phone is designed for a specific market, see the link in my signature "S60v3 Product Codes". The sticker under the battery has a 'CODE' that will tell you what languages are *supposed* to be on that phone; when you use Nokia's firmware upgrader (aka "NSU") it will always look for the proper upgrades.
You *can* flash a firmware from one product code onto another phone, this is what is usually referred to as 'grey market' phones. Someone got a bunch of them from some place (say, India) and reflashed them with a different firmware (say, Malaysia). When you try to upgrade the phone later with NSU, it will try and upgrade the firmware that's supposed to be on it.
NOTE: most all firmwares have English UK or US on them in addition to their other languages (Chinese, Filipino, Thai, Spanish, etc.).