If I recall, Telus voicemail for mobility plans is 3 messages for 3 days. The service is meant to allow response to messages left in short order. If you have an iPhone, you can use Visual Voicemail to have messages delivered to your phone. If you have need for more message space, or longer hold times, there is an add-on with 25 voicemails for 25 days, or another to convert voicemails to text. See: Shop > Add-ons for more info.
It depends what plan/add ons you have like @NFtoBC said. A lot of the new plans have the voicemail 25 built in. You may be on an old plan. If you have of the voice only plans they only have the voicemail 3 which is the one where it's only 3 voicemail for 3 days. Iphone visual voicemail actually comes with 25 voicemail built into it for $5 monthly. Or you could do voice to text if you prefer which also has the option to email your voicemail to yourself so you always have them 🙂