A long winded reply ...
Coast to coast to coast to coast wireless coverage depends on a few factors. Hardware of course plays an issue, but perhaps more important is the service provider. (Hey - this is TERB. I'm allowed to talk about SPs right?

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Of the major providers in Canada (Bell, Rogers AT&T and Telus), all can claim coast to coast coverage in at least analogue mode. If you want digital all the way, you won't really find it. Each provider drops to analogue in some parts of the country.
Bell & Telus use a system known as CDMA/1XRTT. Rogers is switching from TDMA (somewhat similar to CDMA technically) to GSM/GPRS. This is a key factor because North America is largely CDMA. In other parts of the world, notably Europe & parts of Asia the standard is GSM. So if you want to buy a phone and take it to Europe with you, you may want to consider Rogers. On the other hand, if North American coverage is important, CDMA is still the superior choice.
It's true that some US carriers are building GSM networks in the major centers. But when I spoke with a sales rep from Rogers, he couldn't (wouldn't) verify US coverage for me out side of the major cities. On the other hand, I know from experience that CDMA works fine here and in the US. Rogers will claim that their GSM/GPRS network equals their older TDMA network. That's not quite true - if you question them on the finer technical points you'll find that GSM is roughly 80% current coverage and is unlikely to exceed 95% in the near (6 months) future. Beyond 12 months GSM will likely equal or exceed current TDMA coverage though.
At the COMDEX show this past week in Toronto, I attended a session which discussed the differences between CDMA & GSM. The bottom line was that as we move to the next generation of cell phone services (3G and beyond) neither CDMA nor GSM will be able to handle the true broadband requirements. Yes, I know that 3G phones are supposed to go up to 2 Mbps eventually, but the truth of the matter lies in a technical analysis of how the networks are set up to handle voice calls and data calls. Without going into a lot of details, a cell (2.5G and/or 3G) is set to grant some bandwidth to voice, and the rest to data. So even though the networks can theoretically handle up to 2 Mbps, the reality is that they won't becuase they're too busy trying to do 2 things at once.
Bottom line on SPs - North America is CDMA with a trend towards building a competing GSM network over the next 2 or 3 years.
From a cost perspective, I can only really comment on Bell which has a Digital North America plan starting around $99. This includes calls from anywhere in North America to anywhere in North America anytime of the day. If you go to bellmobility.com and search rate plans for DNA you should be able to find more details. Rogers of course has a competing plan which costs exactly the same.
There are other plans which include long distance rates if you call from Canada to the US, but not the other way around. I think the Bell plan is RealTime Canada, but I'm not sure about that.
In terms of hardware, you'll find dual band phones and tri mode phones. For more seamless coverage, tri bands are better and usually slightly more expensive. In North America there are currently 3 frequencies available to cell phone users - 900MHz analogue, 900MHz digital and 1.9GHz digital. Dual band phones usually pick up only 900 MHz analogue & 1.9 GHz digital. Tri mode of course picks them all up.