Nepal Telecom doesn't have much in terms of roaming agreements with other telecom companies.
What you do in Nepal is to rent a local phone (try at Fulbari Resort, or perhaps a private communications/computer companies) or buy a card phone.
As a short-term visitor you'll be fine without a mobile - there are so many nice communications shops around in Pokhara that will be pleased to organise your calls home or wherever at a modest rate. But a mobile is unbeatable when it comes to organising things, setting up appointments and adjusting schedules on the run in Nepal, such as work, expedition or working out logistics for a major trek.
Mobiles work in Pokhara, and as long you are less than, say 20 kms away and within the sightline of the city and its antennas, then you will have a connection. There are holes in the coverage, and for instance the central part of Lakeside is outside range.
Luggage and bags:
A day pack fopr town trips and day hikes.
A backpack for independent lodge trekking - 60-70 L should be suffcient.
Clothing/Shoes/Weather Gear: Light trousers for around town and trekking.
Light shirts and short-sleeveds for town and trekking.
Lightweight rain/wind profis
Lightweight hiking boots, a pair that can get you through some mud.
Sandals that stay on in water.
Sun/combined rain hat.
Long underwear (lighweight stuff, wool or synthetics) for winter use.
Toiletries and Medical Supplies: There are many mosquitos in Pokhara; bring a good repellent!
There will be leeches waiting for you along the trail when hiking during/after rain. Salt will put them off. A desinfectant liquid or cream will keep bites, wounds and scratches from going septic. Bring band aids as the things locally available isn't too good.
Photo Equipment: From Pokhar and Lakeside itself there are potentially splendid views of the mountains; bring binoculars and telephoto lens for your camera. Film is available in the main tourist-geared supermarkets on central Lakeside.
Camping/Beach/Outdoor Gear: A lightweight zippered sleeping bag for lodge trekking and winters in Pokhara. Can be rented locally.
Water bottle - I like the flexible Platypus ones.
If camping on your own, a lightweight tent and sleeping pad such as a 2/3 length light thermarest or so will do.
Miscellaneous: For treks up to more than 2000 meters during the winter (Dec-mid Feb) bring clothing that can save you through freezing temperatures during night. Snow will fall in places like Siklis and Poon Hill.
If you will depend on local water, bring a small water filter or at least purifying tablets.
Luggage and bags:
Actually one can buy everything there...
Clothing/Shoes/Weather Gear: Raincoat (a portable one, so that you can always carry it on with you - as you never know when it's gonna rain), good walking shoes (as well as sandals), shower shoes
Toiletries and Medical Supplies: Yeah, I always take toilet paper with me. :-)
Medical supplies - definitely something against malaria (I had bought the medicine in India - it's called Sudarshan - black, bitter tablets). It's good to have something against fever and stomache ache. I prefer natural medicine, so I bought most of the stuff in India, in ayurvedic stores...
Photo Equipment: I had an idiot camera and I regret it now. But on the other hand, travelling with a good camera would be risky (we had a sand storm in Kali Gandaki gorge).
Miscellaneous: Take a cigarette lighter to burn off the leeches! There is a local plant, which if you take the leaves and crush and rub them over your feet (or any other place that might be bitten) will prevent leeches from biting you. It does turn your feet green, but is better than being bitten. Locals will be able to tell you which plant to use.