If you already use a BlackBerry handheld from Research In Motion (RIM) it probably won't take much to sell you on the new BlackBerry 7780, the latest trimode GSM/GPRS color model, a combination cell phone, e-mail retrieval and wireless Web browsing device.

The BlackBerry 7780 and almost identical 7750 (CDMA) and 7730 (GSM/GPRS) are a further refinement on the already popular BlackBerry product line. (RIM now boasts over one million subscribers worldwide.) The big improvement with these new models: a larger, higher-resolution color screen.

We recently had a chance to play with the 7780. We were impressed. In fact, we're hard-pressed to find anything to complain about.

The 7780 was announced at the beginning of June and, as of writing, is only available so far on the Rogers Wireless network in Canada. It works on 850 and 1900 MHz networks in North America and 1800 MHz networks in Europe and Asia Pacific. Rogers sells it for about $450 with a one-year plan, $375 with a two-year plan.

The virtually identical 7750, announced in May, is a Dual Band, single mode CDMA2000 1X and cdmaOne phone that works on 800/1900 MHz networks in North America. RIM initially said that Verizon would sell it, but the wireless carrier doesn't appear to be doing that yet. The 7750 is available on the Telus Mobility network in Canada.

The 7730 is a Tri-Band GSM/GPRS device that works on 1900 MHz networks in North America and 900/1800 MHz in Europe and Asia Pacific. RIM announced that T-Mobile would offer it, but again, T-Mobile doesn't appear to be selling it yet.

The three models are otherwise virtually identical - although the 7780 and 7730 do come with 16 MB of flash memory versus 14 MB for the 7750. And the 7780 and 7730 are enabled for roaming between North America and Europe or Asia, while the CDMA 7750 is not.

All have a slightly larger foot-print than previous BlackBerry PDA phones - 4.76 inches long by 3.03 inches wide. This compares to 4.45 x 2.95 inches for their most recent predecessor, the BlackBerry 7510, and 4.4 x 2.9 inches for the earlier 7200 series.

The 77xx models are thinner, though - .71 inches versus 1 for the 7510 and .85 inches for the 7200s - and a whole .85 oz. lighter than the 7510 at 5 oz. (The 7200 units are actually a hair lighter than the 7780.)

These tiny increments go almost unnoticed at first. But most of the increase in length and width is accounted for by the new larger, brighter TFT LCD display - 240 x 240 pixels (2.13 x 2.13 inches) - which supports over 65,536 colors.

Our most recent BlackBerry experience was with the monochrome 6210, an impressive product in its own right. The 7780 screen makes for a surprisingly big improvement on the 6210.

Because the text is noticeably higher resolution - and because the new sans serif typeface is very well designed - it's much easier to read text on the 7780 screen.

Color also makes it possible to refine screen layouts so that it's easier to view and to find things at a glance. The larger screen dimension also means there is now room for all of the standard function icons on the home screen.

These may seem small things - and in and of themselves, they are - but the easier a smartphone is to use, the more natural it becomes and the more productive you'll be with it.

Color also makes for better handheld games of course, including the pong-related BrickBreaker game that shipped with this product.

The player fires a projectile at an arrangement of colored rectangles at the top of the screen. When it hits, they change color or disappear - the object is to knock them all out. The projectile caroms back down to the bottom of the screen where the player has to move a paddle (using the BlackBerry thumbwheel) to bounce it back at the rectangles.

Web sites such as Handango have other downloadable color games for the BlackBerry platform, ranging in price from $2.50 to $15. You can also try out software for free from RIM Road's software section.

Despite the bigger, higher-resolution color screen, RIM claims to have held the line on battery life - five hours of talk time and nine days of standby time. Results are almost never as good in real life. We were unable to test battery life conclusively, but in past tests of other BlackBerry products, we've found the company's claims are not wildly exaggerated.

In most other respects, the 7780 functions much as the earlier 6210 and other BlackBerry smartphones.

It offers basically the same array of communications functions. E-mail is pushed from an Exchange server or redirected from an existing e-mail account, so you never have to remember to retrieve mail. It just arrives, wherever you are in the service providers coverage area.

This was the original reason, and is still one of the most compelling, for using the BlackBerry platform and service.

E-mail functions have for some time included the ability to read attachments sent in popular formats such as Microsoft Word, Excel and PowerPoint, WordPerfect and HTML. This is neither a 7780 nor a BlackBerry exclusive, but for users hooked on the platform it was a very welcome enhancement.

The device also works as a WAP (Wireless Application Protocol)-based Web browser - where service is available from carriers. The Rogers service is very slick with a wealth of choices for news, sports, weather and other Web information formatted for small screens.

Besides somewhat improved readability, the larger color screens don't make a huge difference yet to the Web browsing experience - though it seems reasonable to expect WAP page makers will eventually exploit the color and larger text capacity.

As with earlier models, you can use the 7780 as a phone in two ways. It has integrated microphone and speaker so you can hold it to your ear and speak. In our tests with the Rogers network, voices were clear - though I needed to turn the volume up full to get a comfortable level.

The product also comes with a hands-free earbud phone that you plug into the mini-jack on the top edge of the device. The microphone is built into the cord and dangles in the vicinity of your mouth. Voice and connection quality using the earbud phone were also more than acceptable in our tests.

The user interface is for the most part unchanged. The keyboard is slightly bigger so the keys are more spread out. The difference is small and we did not see much advantage, though fat-fingered users may welcome the additional real estate.

The number keys, which piggy-back on letter keys on the left side of the screen, are now two-toned - letters printed black on white at the bottom of the key, numbers light on dark at the top. This makes it quite a bit easier to see them. Finding the number keys was a constant problem, we found, with the 6210.

The thumbwheel, used for scrolling, and the Escape key - which also functions as a back-arrow key - are moved closer to the front edge of the device than they were on the 6210 and some other BlackBerrys. While I can see the ergonomic logic - you're not reaching back with your thumb when the thing is cradled in your palm - I again didn't see a huge advantage.

The thumbwheel also had a slightly different, more positive feel and took a little more pressure to turn - or it may have only seemed so because of the slightly altered position and the fact that the unit was brand new. In any case, it should be easy enough to get used to.

A separate Phone button, absent on the 6210 and other earlier BlackBerry PDA phones, is also on the right-hand edge, just above the thumbwheel. It saves scrolling through the icons on the Home page. Clicking it from the Home screen brings up the Use Once dialog - where you use number keys to input a phone number that is not in your address book or list of recently dialed numbers.

The 7780 is not a breakthrough product, but it is a very good smartphone with some intelligent refinements on past models. If you already have a color screen BlackBerry phone, the 7780 may not offer enough to warrant switching, but if you're thinking of moving up from monochrome to color, or switching from another platform, this or one of the other 77xx models would make an excellent choice.