Yes, they could grab a commlink and form a PAN that way. But if they're going through the commlink or deck, they're working as a regular matrix user, and are unable to use any of their resonance abilities. In other words, to be an effective hacker, they have to stop being a technomancer and be a decker.
That isn't my reading. They only lose the ability to use their resonance abilities when they enter the Matrix through a device. You just have to be the owner of a commlink that is the master of the PAN to defend against matrix actions. They are not defending devices with their icon/persona.
I never played a former edition of Shadowrun, so I don't know what I am missing from 4th. I read Unwired and it seems like Streams and Paragons would be nice helps to better customize/specialize/hybridize technomancers that are an easy add and don't know why they weren't part of Data Trails. Complex Form Fade values are also very high for their benefit, but again, that isn't a drastic fix. A sprite being able to share a marks with its technomancer would be very nice:). The big problem with technomancers is that their fluff does not match their crunch. What the book implies they are good at they are not and what they are good at is never really mentioned and seems counter to that fluff. Additionally, they don't have a way to increase meat initiative (though I guess that is supposed to be mitigated by the fact they can max their matrix initiative dice) the way that adepts, magicians, and cybered characters do except with Lightning Reflexes (a big karma sink), getting 'ware, and drugs. I think technomancers and drugs work great together, but it really shouldn't be a necessity. I also like technomancers with 'ware, but as writtenin the fluff, technomancers seem to be ant-ware, but I find that 'ware and compliment/compensate quite a bit without much Resonance loss. I think some kind perk to 'ware use could be helpful and logical for technomancers who are said to have a natural affinity to machines. Perhaps an echo that mimics something like the Burnout's Way could help in this regard.
Below are some Technomancer archetypes that I think work (though perhaps less than previous editions, but I don't have a comparison):
1. Technoshaman/Pet-class:
Playing a with lots of registered sprites brings a lot to both matrix work, legwork, and meatwork. Having a Fault Sprite take out Host IC will you finish hacking, Having Crack Sprites do Matrix Searches for you while you sit in a static veil bubble snooping on someone's commlink all night, loaning out machine sprites to team members who can get a lot out of them, etc. It's definitely a different style of play than other archetypes, more time intensive, but can be a lot of fun. Being able to riskily overcompile a big ol' sprite sometimes is helpful too (ex. Level 12) to get the job done for you. These characters are not going to have the full breadth of hacking chops of deckers, but they don't need them. The have sprites that can do a lot of the work, and just enough complex forms to help them about.
2. Jack of All Trades/Skillwire:
This is another playable option, though I think less fun than some others. Basically picking up a swillwire/skilljack system, Have a machine sprite run diagnostics, and bam, character gets higher dice rolls and limits on every skillsoft. A character like this can have utility both in the meat and the matrix, and if the character keeps a decent Resonance, and still have lots of beefy enough helpful sprites.
3. Techno-Riggers
Technomancers can still make great riggers. Sure, it does take them 30 karma to get a control rig echo and skinlink (for rig and direct connect bonuses), but in the meantime, a machine sprite can plenty of dice pool/limit bonuses to vehicle/gunnery tests. After 30 karma, it could be argued that technomancers could have an edge, as they can do what any mundane rigger could do and have access to sprites/CFs. Further down the road, they could get up to an equivilant control rig 3, which most riggers don't get.
4. Combat-Technomancers
I've played with these before. While on average not quite as fast or big as a street sam and not quite as dodgy as a combat adept (diagnostics on reaction enhancer legality would help with this), they can still be quite lethal. Appropriate, limited 'ware, focused skills, and machine sprites go a long way here. While unlike a combat decker in that they really can't solo hack. Teamed up with a decker, the combat technomancer can provide sprites/action economy to matrix work, still use complex forms (diffusions, resonance veils, etc.) that can make a decker's life a whole lot easier. At 30 karma, they can get a Pain Editor echo. Most characters can only get the real version at character generation with the Restricted Gear quality, as it is tough to get in play, but technomancers can. Jack of all Trades and Drugs go a long way here too pick up low level skills and to increase initiative.
5. Technofaces
A legwork and social infiltration pro. Social and sneak dice boosting armor + Machine Sprites go a long way here. As does having a face that can do their own or have sprites do matrix search tests, simultaneously. Profiler is my favorite quality for these type of characters, as it can leverage matrix search for even higher dice pools for key social rolls. Though possible to make them also be hackers, hacking technofaces are not going to be on par in the matrix as deckers. With skinlink and some hacking skills, getting through locks, adjusting cameras, etc. become easy. They can talk or Resonance Veil their way past suspicious humans and computers alike. Like the combat-technomancer too, they still have a lot to offer the dedicated team decker so they don't have to deal with matrix threats alone.
Note: I agree that the technoshaman/pet-class is really the best way to play a primary matrix specialist. I've been playing with heavily 'wared Resonance 1 more "techno-adepts," technomancers that do their matrix work more like deckers that eschew CFs and sprites in favor of high skills and attributes, but it's admittedly pretty delicate/limited way to build and not for everyone. I have been having a hard time making a high Resonance "Resonancer" work too, a technomancer that uses Complex Forms to do the bulk of their Matrix work and heavily invests in them at character generation, as well as really only focusing on technomancer skills (Tasking group and Software). High Fade and nebulous rules make this tough though. But for example, a Resonancer would use Transcendent Grid instead of grid hopping, Editor instead of Edit File, Puppeteer to invite marks (youch but if this character can't hack, this is the only way into a host), Resonance Veil instead of Hide, Resonance Channel instead of direct connecting (if they do end up hacking), etc. Registered Sprites would be use to sustain complex forms like Diffusions of Matrix Attribute and Resonance Veil. They may not even need the Computer skill as Sprites can do Matrix Perception and and Matrix Search for them. The perk is that they don't need any 'ware/gear, don't have to worry about noise, and can work as fast or slow as they need (no overwatch or awareness of of target on failed tests). They probably won't have much meatworld capability but this is more of a stay at home or in the van hacker. Fade resistance is their biggest challenge, so a character like this will focus on having a high willpower, Resonance, use Willpower boosting drugs, and probably take the Otaku to Technomancer Quality. Again, difficult to make work (I am still working), but perhaps another way to make a Technomancer Matrix specialist.
The other ways (perhaps a the skillwire one could also do matrix work if need be, but that is kind of that role anyway) hybridize into other areas but can provide really helpful matrix support. Though the fluff doesn't indicate it, to me it seems that Technomancers play best as taking non-matrix specialties (combat, rigging, face, etc.) and providing Matrix support. Matrix specialists take on a lot of pressure as hacking is stressful, solitary, and can go south real quick. Being able to have a dedicated team decker AND a matrix support technomancer can make matrix work more interesting, less solitary, and hopefully more fun and more successful too! I will also note that adepts tend to be better at their specialties than hybridized technomancers, but technomancers can have some more flexibility as they grow (Adept power vs machine sprite diagnostics dice pool bonuses: adept powers are fixed and Diagnostics can be used on different devices and for different skill tests), provide matrix support, and are less likely to have their special status easily discovered (adepts can be identified with a single hit on an assensing test vs 5 for technomancers, they have powers that light up in the astral while Resonance effects/sprites are a little more nebulous in their origin, etc.).
Basically, combining the changes to the Matrix, returning to the abomination sacred cow quaint priority system instead of the Point Buy system, and core level alterations to how TMs work all make playing a TM an experience akin to waking up in a hardcore BDSM parlor gagged and without knowing any safewords.
Safewords aren't going to matter much if you're gagged. :-)