Hi Ozirob,
This is from Wiki and I also confirmed with the Cambodia Embassy page. You'll want to get the Ordinary or what most everyone calls a business visa which is 25 USD on arrival the airport. Some people say you need an introduction from a company or proof of business, but I've never heard of them actually asking for that. If they did ask you can just tell them you are looking at business opportunities in Cambodia, but I just don't see that happening, it didn't to me when I came. I just walked up and said I wanted a business Visa and they said 25 USD please.
Anyway a tourist visa can only be extended once for a total of two months, so that won't do you any good if you want to stay for 3 months.
When you get here withing the first 30 days, the earlier the better, you just go to a travel center and give them your passport and the fee for the 3 month visa and withing 2-3 days they will have it back to you with your multiple entry visa. It's so easy!
Most expats use Lucky Lucky Motorcycle, I've used them for 7 years and have never had a problem. Here is their info from the Cambodia Yellow pages They are on street 93 = Monivong. Visa Extension
You will have no trouble getting internet and phone service here in Cambodia, we have a great fiber network and 3G available through several ISP's and phone plans, using a Cambodia sim card, you just need to bring your passport with you once you pick which mobile phone company you want to get your sim card and Cambodia phone # from.
With Cellcard you can pay as you go or pick a monthly plan with different options. Cellcard home page but you can choose from several different cell phone companies.If you have any other questions, just let me know or post to expat-blog.
Cheers
From Wiki
The official price for a tourist visa is US$20, and US$25 for an "ordinary visa" also known more commonly as "business visa". Staff may try to charge more at some land border crossings: hold out for the official price, particularly at major crossings, but don't be upset if you have to pay US$1-2 extra. The major difference between a tourist and an ordinary/business visa is that a tourist visa can only be extended once, for maximum 2 months of stay in Cambodia, whereas an ordinary/business visa can be extended for extended periods up to a year and more.
Visas can be obtained at Cambodian embassies or consulates. Visas are also available "on arrival" at both international airports, all six international border crossings with Thailand, some international border crossings with Vietnam, and at the main border crossing with Laos.
Tourist visas: all are valid for one stay of up to 30 days. Those issued in advance expire 90 days after issue. In Phnom Penh (or elsewhere via agencies), tourist visas can be extended only once, allowing an additional 30 days at a cost of around US$30.
Visa-E, Ordinary or Business visa this is the best choice for those wishing to stay for over two months with multiple entries, as a business visa can be extended indefinitely (approximately US$155 per 6 month extension and US$290 per 12 month extension) and have multiple entry status when (and only when) extended. Most Phnom Penh travel agencies process the extensions. , once you are in possession of a long-term Business Visa, travel into and out of the country is very convenient and painless.