Risks are much the same as many other countries in Africa and significantly less than some, including parts of South Africa. Nevertheless muggings, robberies, rape and murder do occur, so the normal precautions should be taken. Women absolutely should never walk alone on beaches, in recent years, attacks on women have grown in tourist areas. In particular it's worth checking with local hostels and other travelers as to where dangerous areas are.
But in general the Mozambican people are extremely warm and friendly and you will encounter far less hassle than in almost all of the countries surrounding it.
Internet is widely available in Maputo, with many internet cafes and all major hotels having internet access. Both mCel and Vodacom have introduced internet to cellphone and USB modems. See above for further information. Outside Maputo internet coverage is sporadic and mostly available in places frequented by tourists. Local Telecommunication de Mozambique TDM offices almost always have internet although speed and availability can be problematic.
mCel (http://www.mcel.co.mz/) is the state-owned provider, and as of yet the government has only licensed one other company, the South-African owned Vodacom Mozambique (http://www.vm.co.mz/). Apparently a third is arriving shortly. GPRS data and internet are available on mCel, with 3G in Maputo and other main cities. The APN for Internet is isp.mcel.mz and for WAP it is wap.mcel.mz with an IP address 10.1.4.35. Vodacom have 3G in many towns and GPRS Edge elsewhere. The APN is internet. Check your phone manual for setting instructions. The mCel service is not entirely reliable, especially outside Maputo. Vodacom is generally very good. While it is OK to buy credit from the hundreds of vendors roaming the streets wearing mCel or Vodacom shirts you should never buy SIM cards / starter packs, in many cases they sell them at hugely inflated prices and often they will be from one of the many recalled batches that no longer work. Any mobile phone store can sell you a working starter pack for around 50Mts.
The official language of Mozambique is Portuguese, though many people speak English in the capital Maputo and in touristy areas. The further north you travel the less likely you are to encounter English speakers, and as you enter more rural areas even Portuguese is limited.
Swahili is useful in the far north of the country as you get close to Tanzania, especially along the coast, and Nyanja is spoken near the border with Malawi and Zambia. Some native words from the Shona language can be useful if you are traveling near Cabora Bassa.
In Mozambique the police do not exist to help you, only to try and extort money of you. Do not trust them under any circumstances.
Insisting to be taken to a police station is unlikely to improve your situation, with the exception of in Maputo, the police have been known to rob tourists blind and throw them in a cell. Instead mention contacting your embassy or the anti-corruption hot line to verify a fine and always ask for a receipt.
If you have cause to go to a police station EG - Filing a police report for insurance purposes after a theft do not take any valuables or excessive currency with you and try to always go with someone else.
While most of the country has been cleared there is still an on-going risk in rural areas away from the EN1 in Sofala, Tete, Manica, Gaza, Inhambane and Maputo provinces. It should be noted that only 2 or 3 incidents a year occur with landmines and they are all well outside the tourist trail.