All inbound links are good links. Every link from a page that is actually in the Google index will award some amount of PageRank, no matter how small, and will provide Link Reputation through the text that is used with the link. Just be sure to get the correct link text in the links that point to your pages.

I have not been able to measure any difference between these two stategies. On purely theoretical grounds the single focus linking should edge out the other approach all other things being equal. But on the other hand, no page lives on a single search phrase alone. And furthermore, the difference between the two I am certain is very minor. Sooo, I would think that multiple related terms is okay, and possibly even better.

That said, I would use a "noise word" connective like so: "cell phones and phone accessories" simply because it reads better to humans than "cell phones, phone accessories".

In all cases, make sure the phrase has no intervening words, like "cell phone plans and accessories" does not work as well for both phrases as does "cell phone plans and cell phone accessories" simply because the engines like to see the phrase contiguous instead of interrupted by other words.

There is no right answer to this other than to measure what is currently working in the search engines — that’s what OptiLink is for. At Google, the on-page density carries almost no importance. As long as you get the keywords in the title tag, just about every other aspect of ranking is Link Reputation analysis or PageRank.

Probably both, with title being the more important of the two. Google appears to rely almost exclusively on the title in terms of on-page factors.

There are a number of techniques I recommend to clients depending on specifics, but, while it may look good, in no case is a graphical link a good ranking tool. Because the engines do not appear to use the alt text of an image to influence Link Reputation, the image link serves to dilute the reputation of the targeted page. I would always make these nofollow links and provide a separate text link, or include text along with the image in the same link — that does appear to work — and then style it using CSS so it looks decent.

It is pages themselves that actually create PageRank. Links just spread it around. So to get high PR on one page, will require that you give up PR somewhere else, or you get links from other sites. There is no linking strategy that will "create" PR.

That said, the linking structure you use is critical to controlling where PR gets concentrated. This is the subject of the Mastering PageRank video.

In one word, no. Every page at Google is ranked by itself, not as part of a collection of multiple pages from a single site. It may be that the spidering of a site for inclusion into the index involves heuristics that depend in part on the number of pages already found on the site, but I have not seen such an effect.

That said, the goal is to have lots of pages to use to build PageRank and Link Reputation.  You can have those pages on one site, or on several. It does not matter, so long as you build the pages.

That would be diluting, not strengthening. Strong reputation is where all the links say the same thing. If they say different things, it weakens the original reputation in return for, equally weak, reputation on the additional terms.

But there isn’t anything inherently wrong with ‘weak’ reputation, just as a slow runner can win a race if only slower runners show up, a weak reputation might be enough if the other pages are weaker still.

Use optilink to measure the number and quality of links for the top pages, account for the other factors like page title and page rank, and make a decision. Often, you will find that additional pages focused on your additional terms is a better solution, but not always.