I guess he answered these, but to reiterate, for the most part--
* Mmissionaries get to email home once a week. I think that's their only internet access, i.e. no web surfing or jazzfanz-ing. (Or TV watching, for that matter.) Also, they can receive email from anyone,
but can only email their own family. As far as I know, as far as regular mail goes anything is fine--the missionary can receive as many letters as people will write him, and can write letters back (as far as time permits).
* Many missionaries are issued cell phones these days, undoubtedly to be used for local missionary-related calls only.
* Writing a missionary to give him game/team updates is perfectly fine, and would likely result in much rejoicing on the missionary's part.