There is no single cell phone prefix for the USA. Most cell phones are given numbers with the local area code of their owner.
The country prefix for Romania is 0040.
Most people in the US have a cell phone.
Just like you would to any other place - by using the right telephone number. For instance if you're texting from the UK to a US phone, you need to use the US country code, and to drop the first zero in the cell phone prefix. If you're texting to a UK phone in the US, simply use the same number as if the phone was in the UK. The network jeeps track of where the phone is. Note that some contracts and prepaid phones might not allow international traffic.
Dial +1 (including the plus symbol), followed by the 10-digit US telephone number.
No - usually the mobile networks will do all the 'hard work' for you.
You can, but it costs extra money from your account.
In the US it is only AT&T.
Yes you can if you are on a mexican sim card/network. It is possible to text if both are on the same us network but you need signal for that network.
Verizon wireless, Sprint, and ATT
yes
No, you do NOT have to purchase a replacement phone from US Cellular. I have included a link below to an online cell phone store that sells US Cellular cell phones. Hope this helps.
There is not difference - just a persons preferrance in what they call it. In Europe, they use the term mobile phone more and in the US we call it cell phone.